In-plane switching liquid crystal display with bent electrodes

An in plane switching liquid crystal display (2) includes a first substrate (27), a second substrate (37) and a liquid crystal layer (23) having a plurality of liquid crystal molecules. A number of pixel electrodes (25) and common electrodes (24) are formed on the first substrate, and each of the pixel electrodes and common electrodes include at least two bend portions (241, 242, 243). Each bend portion has a first side and a second side. An original alignment direction of the liquid crystal molecules form at least two different angles with the sides of the bend portions of the common and pixel electrodes. When a voltage is applied to the pixel electrodes and the common electrodes, the liquid crystal molecules are aligned along at least three different directions. Therefore, the IPS-LCD can have uniform viewing performance at different viewing angles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to in plane switching liquid crystal displays, and particularly to an in plane switching liquid crystal display which can provide uniform viewing performance at different viewing angles.

2. General Background

Liquid crystal displays (LCDs) are typically used as the information display in various devices such as computers and vehicle and airplane instrumentation. One type of LCD called the twisted nematic liquid crystal display (TN-LCD) often has the drawback of a narrow range of viewing angles. Thus an improved design called the in plane switching liquid crystal display (IPS-LCD) has been developed in order to provide a broad range of viewing angles. The IPS-LCD typically has a plurality of common electrodes and a plurality of pixel electrodes all disposed on a same substrate of two opposite substrates, for driving liquid crystal molecules contained in a liquid crystal layer between the two substrates The resulting electric field is substantially planar and parallel to surfaces of both substrates. The IPS-LCD typically has a broad range of viewing angles.

According to the particular electrode array of its pixel electrodes and common electrodes, an IPS-LCD is classified as a single-domain type or a two-domain type.FIG. 7is a top plan view showing an electrode array of a pixel area of a conventional single-domain IPS-LCD1. Two parallel gate lines11are orthogonal to two parallel data lines12, thereby defining the rectangular pixel area. A thin film transistor16, a plurality of common electrodes141, and a plurality of pixel electrodes151are formed in the pixel area. The common electrodes141and the pixel electrodes151are strip-shaped, and are arranged parallel to each other in alternating fashion. When a voltage is applied to the common electrodes141and the pixel electrodes151, a horizontal electric field is produced therebetween. Long axes of the liquid crystal molecules are aligned parallel to the direction of the electric field. As a result, an amount of light passing through a liquid crystal layer (not shown) to display images can be controlled.

However, the conventional single-domain type IPS-LCD1has the following problem. Since the common electrodes141and the pixel electrodes151are all strip-shaped, the electric field is distributed along one direction only. When the displayed image is viewed at different oblique angles, an observer can frequently notice a quite large color shift.

In order to solve the above-mentioned problem, the two-domain type IPS-LCD has been developed.FIG. 8is a top plan view showing an electrode array of a pixel area of a conventional two-domain type IPS-LCD10. Common electrodes142and pixel electrodes152are designed to have a bent shape in the pixel area. Referring toFIG. 9, when no voltage is applied to the common electrodes142and the pixel electrodes152, the liquid crystal molecules are aligned along a direction A. When a voltage is applied to the common electrodes142and the pixel electrodes152, two electric fields E10and E20having two different directions are generated between the pixel electrodes152and the common electrodes142. Accordingly, liquid crystal molecules are rotated in two different directions to form two light transmission regions in the one pixel area. The IPS-LCD10exhibits a two-domain display effect. As a result, different colors can be seen in the two regions when the display screen is obliquely viewed. Since the colors compensate for each other, the color shift in the two-domain type IPS-LCD10is reduced.

However, the two-domain electrode configuration of the IPS-LCD10still inherently limits the display thereof. Even better visual performance at various different viewing angles is desired.

What is needed, therefore, is an IPS-LCD which has fine viewing characteristics in different viewing directions.

SUMMARY

An IPS-LCD includes a first substrate and a second substrate disposed opposite each other and spaced apart a predetermined distance. A liquid crystal layer having a plurality of liquid crystal molecules is interposed between the first substrate and the second substrate. A plurality of gate lines and data lines are formed on the first substrate, to define a plurality of pixel areas. A plurality of pixel electrodes and common electrodes are formed on the first substrate, each of the pixel electrodes and the common electrodes includes a plurality of bend portions, each of the bend portions has a first side and a second side. The first sides and the second sides are along at least three different directions.

When a voltage is applied to the pixel electrodes and the common electrodes, the liquid crystal molecules are aligned along at least three different directions. Accordingly, each pixel area is divided into at least three different regions each having a respective viewing characteristic. The IPS-LCD has good visual performance at various different viewing angles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIGS. 1-2, an IPS-LCD2of a first embodiment of the present invention includes a first substrate27, a second substrate37, and a liquid crystal layer23having a plurality of liquid crystal molecules. The first substrate27and the second substrate37are spaced apart from each other, and the liquid crystal layer23is disposed therebetween.

A color filter20and an alignment film39are formed on an inner surface of the second substrate37in that order from top to bottom, and a polarizer38is attached on an outer surface of the second substrate37.

A polarizer28is attached on a lower surface of the first substrate27. A polarizing axis of the polarizer28is perpendicular to that of the polarizer38. A plurality of common electrodes24and a plurality of pixel electrodes25are formed at the first substrate27, with an insulating layer40disposed between the common electrodes24and the pixel electrodes25. A plurality of data lines22are formed on the insulating layer40. A passivation layer50is coated on the insulating layer40, and covers the data lines22and the pixel electrodes25. An alignment film29is formed on the passivation layer50, for orientating the liquid crystal molecules. The insulating layer40and the passivation layer50are made of silicon dioxide (SiO2) or silicon nitride (SiNx).

A plurality of gate lines21and a plurality of the data lines22are cross-arranged on an inner surface of the first substrate27, thereby defining a plurality of pixel areas. Each pixel area comprises a thin film transistor26disposed at an intersection of one of the gate lines21and one of the data lines22. The thin film transistor26comprises a gate electrode261, a source electrode262and a drain electrode263, which are connected to the gate line21, the data line22and the pixel electrode25respectively. Each pixel area further comprises a common electrode bus line240connected to the common electrode24, and a pixel electrode bus line250connected to the pixel electrode25.

The common electrode bus line250and the gate line21are formed at a same level parallel to each other. The pixel electrode bus line250is formed above the common electrode bus line240, and covers part of the common electrode bus line240. A storage capacitor is defined between the pixel electrode bus line250and the part of the common electrode bus line240which is covered by the pixel electrode bus line250.

The common electrodes24are zigzagged, and extend obliquely at a same angle from the common electrode bus line240. Each common electrode24comprises a first bend portion241, a second bend portion242and a third bend portion243successively arranged end-to-end. The pixel electrodes25have a similar shape to the common electrodes24, and extend obliquely at a same angle from the pixel electrode bus line250. Thus the common and pixel electrodes24and25are arranged parallel to each other and in alternating fashion. The common and pixel electrodes24and25are made of a transparent conductor, such as indium tin oxide (ITO) or indium zinc oxide (IZO). When a voltage is applied to the common electrodes24and the pixel electrodes25, horizontal electric fields are produced therebetween. Long axes of the liquid crystal molecules are aligned parallel to the directions of the electric fields.

Referring toFIG. 3, the first bend portion241, the second bend portion242and the third bend portion243comprise first sides2411,2421,2431and second sides2412,2422,2432respectively. All the first and second sides2411,2421,2431,2412,2422,2432have a same length. The first sides2411,2421,2431are not parallel to each other, but instead are aligned along three slightly different directions. The second sides2412,2422,2432are not parallel to each other, but instead are aligned along three slightly different directions.

When no voltage is applied to the common electrodes24and the pixel electrodes25, the liquid crystal molecules are aligned along an original direction as shown by arrow B under the effect of the alignment films29and39. Since the first sides2411,2421,2431and the second sides2412,2422,2432are aligned along six different directions, they form six different angles with respect to the original alignment direction. Thus when a voltage is applied to the common electrodes24and the pixel electrodes25, six electric fields E1, E2, E3, E4, E5, E6along six different directions are produced between the common electrodes24and the pixel electrodes25. The electric fields E1, E3, E5define acute angles with respect to arrow B, and the electric fields E2, E4, E6define obtuse angles with respect to arrow B. Accordingly, the electric fields E1, E3, E5drive the liquid crystal molecules to rotate clockwise, and the electric fields E2, E4, E6drive the liquid crystal molecules to rotate counterclockwise. As a result, the liquid crystal molecules are aligned along six different directions. That is, each pixel area is divided into six regions, each having respective viewing characteristics. Therefore, the IPS-LCD2provides fine visual performance at various different viewing angles.

In an alternative embodiment, the data lines22can have a zigzagged shape, comprising three bend portions corresponding to the three bend portions241,242,243of the common electrodes24respectively.

Referring toFIG. 4, an IPS-LCD3of a second embodiment of the present invention is similar to the IPS-LCD2of the first embodiment. A common electrode34comprises a first bend portion341, a second bend portion342and a third bend portion343, each of which has a first and a second side. Lengths of first sides3411,3421,3431of the three bend portions341,342,343progressively decrease from a common electrode bus line340. The second sides3412,3422,3432have same lengths as the first sides3411,3421,3431respectively. The first sides3411,3421,3431are all aligned along a first direction. The second sides3412,3422are both aligned along a second direction, and the second side3432is aligned along a third direction. The pixel electrodes35have essentially the same shape as the common electrodes34.

When no voltage is applied to the common electrodes34and the pixel electrodes35, the liquid crystal molecules have a same orientation. When a voltage is applied to the common electrodes34and the pixel electrodes35, three electric fields (not labeled) along three different directions are produced. As a result, the liquid crystal molecules are aligned along three different directions. That is, each pixel area is divided into three regions, each having respective viewing characteristics. Therefore, the IPS-LCD3provides fine visual performance at various different viewing angles.

Referring toFIG. 5, an IPS-LCD4of a third embodiment of the present invention is similar to the IPS-LCD3of the second embodiment. A common electrode bus line440connects common electrodes44. Each of common electrodes44has first, second and third bend portions441,442,443. First sides (not labeled) of the first, second and third bend portions441,442,443are all parallel to a first direction. Second sides (not labeled) of the first, second and third bend portions441,442,443are aligned along second, third and fourth directions respectively. Each of pixel electrodes45has the same shape as the common electrodes44. The IPS-LCD4has a four-domain display effect, and therefore can provide even finer visual performance at various different viewing angles compared with the IPS-LCD3. The length of the first sides and the second sides of the first, second and third bend portions441,442,443decreases gradually with increasing distance away from the common electrode bus line440.

Referring toFIG. 6, an IPS-LCD5of a fourth embodiment of the present invention is similar to the IPS-LCD2of the first embodiment. However, in the IPS-LCD5, common electrodes54and pixel electrodes55are formed at a same level, in order to generate true in-plane electric fields. Other components like the polarizers28and38, the substrates27and37, the alignment films29and39, and the color filter20and the passivation layer50are disposed in the same way as in the IPS-LCD2.

In further alternative embodiments of the present invention, an IPS-LCD can be appropriately structured so that electric fields generated between the pixel electrodes and the common electrodes are aligned along 5 different desired directions, 7 different desired directions, or another desired number of desired different directions.