Multi-domain vertical alignment liquid crystal display having two sub-pixel regions

An exemplary multi-domain vertical alignment LCD (200) includes a common electrode, a pixel electrode and a liquid crystal layer sandwiched between the common electrode and the pixel electrode. The LCD is regularly divided into a plurality of frist and second sub-pixel regions (250, 260). The first sub-pixel region corresponding to two of the first protrusions (241), one of the second protrusions (242), one of the first slits (281), and two of the second slits (282), a second sub-pixel region corresponding to two of the third protrusions (243), one of the fourth protrusions (244), one of the third slits (283), and two of the fourth slits (284), a first ratio of first distance between the first slit and the second slit to a first width of the first slit is less than second ratio of second distance between the third slit and the fourth slit to second width of the third slit.

FIELD OF THE INVENTION

The present invention relates to vertical alignment liquid crystal displays (LCDs), and particularly to a eight-domain vertical alignment liquid crystal display having two different sub-pixel regions in each pixel region thereof.

GENERAL BACKGROUND

Since liquid crystal displays are thin and light, consume relatively little electrical power, and do not cause flickering like in cathode ray tube (CRT) displays, they have helped spawn product markets such as laptop personal computers. In recent years, there has also been great demand for liquid crystal displays to be used as computer monitors and even televisions, both of which are larger than the liquid crystal displays of laptop personal computers. Such large-sized liquid crystal displays in particular require that an even brightness and contrast ratio prevail over the entire display surface, regardless of observation angle.

Because the conventional twisted nematic (TN) mode liquid crystal display cannot easily satisfy these demands, a variety of improved liquid crystal displays have recently been developed. They include in-plane switching (IPS) mode liquid crystal displays, optical compensation TN mode liquid crystal displays, and multi-domain vertical alignment (MVA) mode liquid crystal displays. In multi-domain vertical alignment mode liquid crystal displays, each pixel is divided into multiple regions. Liquid crystal molecules of the pixel are vertically aligned when no voltage is applied, and are inclined in different directions when a voltage is applied.

Referring toFIG. 4, a typical multi-domain vertical alignment liquid crystal display (LCD)100includes a first substrate110, a second substrate120parallel to the first substrate110, and a liquid crystal layer130sandwiched therebetween. The liquid crystal layer130includes a number of liquid crystal molecules130having negative dielectric anisotropy.

The first substrate110assembly includes an upper polarizer112, a first transparent substrate111, a color filter113, a common electrode115, and a first alignment film114arranged in that order from top to bottom. The first substrate110further includes a number of first protrusions141. Referring also toFIG. 5, the first protrusions141are arranged at an inner surface of the first alignment film114along generally V-shaped paths. The color filter113includes a number a red filters (not shown), a number of blue filters (not shown), and a number of green filters (not shown) sequentially arranged in that order.

The second substrate120assembly includes a lower polarizer122, a second transparent substrate121, a number of pixel electrodes127, and a second alignment film124arranged in that order from bottom to top. The second substrate120further includes a number of second protrusions142. The second protrusions142are arranged at an inner surface of the second alignment film124along generally V-shaped paths. The first protrusions141and the second protrusions142are arranged alternately.

Referring toFIG. 5, when the LCD6is in an off state, the liquid crystal molecules131are oriented perpendicular to the first substrate110. In operation during the off state, incident light beams become linearly-polarized light beams after passing through the lower polarizer122. Because the light beams transmit along the long axes of the liquid crystal molecules131, after the linearly-polarized light beams pass through the liquid crystal layer130, the polarizing directions of the linearly-polarized light beams remain unchanged. Thus the linearly-polarized light beams cannot pass though the upper polarizer112, which has a polarizing axis perpendicular to that of the lower polarizer122. As a result, the LCD100displays a black image.

Referring toFIG. 6, when the LCD100is in an on state, voltages are applied thereto, and voltage differences between the common electrode115and pixel electrodes127generate electric fields perpendicular to the first and second substrates110,120. Because the liquid crystal molecules131have negative dielectric anisotropy, they are inclined to become oriented parallel to the first substrate110. Further, the protrusions141,142affect the orientations of the liquid crystal molecules131, such that the liquid crystal molecules131form inclined alignments perpendicular to the slopes of the protrusions141,142. Referring also toFIG. 7, the liquid crystal molecules131orient in four directions A, B, C and D.

In operation during the on state, incident light beams become linearly-polarized light beams after passing through the lower polarizer122. Because of birefringence of the liquid crystal molecules131and the electric fields, the polarizing directions of the linearly-polarized light beams change to align with the polarizing axis of the upper polarizer112after passing through the liquid crystal layer130. Accordingly, part of the light beams pass through the upper polarizer112. Therefore, the LCD100displays an image with desired brightness.

Because the liquid crystal molecules131are oriented in four directions A, B, C and D, color shift that would otherwise be manifest in images displayed by the LCD100is compensated. In particular, the LCD100has a more even display performance along four different viewing directions corresponding to the directions A, B, C and D. That is, the LCD100attains a display having four domains.

However, the four-domain configuration can only compensate visual performance in four directions.

What is needed, therefore, is a multi-domain vertical alignment LCD having more domains that can provide a uniform display in more viewing directions.

SUMMARY

In one preferred embodiment, a multi-domain vertical alignment LCD includes a first substrate including a first transparent substrate, a common electrode formed at an inner surface of the transparent substrate, and a plurality of first, second, third, and fourth protrusions arranged at an inner surface of the common electrode; a second substrate including a second transparent substrate; a pixel electrode formed at an inner surface of the second transparent substrate; a plurality of first, second, third, and fourth slits defined in the pixel electrodes; and a liquid crystal layer sandwiched between the two substrates. A plurality of pixel regions is regularly defined by the two substrates and the liquid crystal layer sandwiched therebetween. The pixel regions are arranged in a regular array, and each pixel region includes a first sub-pixel region and a second sub-pixel region. The first sub-pixel region corresponds to two of the first protrusions, one of the second protrusions, one of the first slits, and two of the second slits, and is divided into four domains by the first and second protrusions and the first and second slits. The second sub-pixel region corresponds to two of the third protrusions, one of the fourth protrusions, one of the third slits, and two of the fourth slits, and is divided into four domains by the third and fourth protrusions and the third and fourth slits. A first ratio of a first distance between the first slit and each of the second slits to a first width of the first slit is less than a second ratio of a second distance between the third slit and each of the fourth slits to a second width of the third slit.

Other novel features, advantages and aspects will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe preferred and exemplary embodiments in detail.

Referring toFIG. 1andFIG. 2, part of a multi-domain vertical alignment LCD200according to a first embodiment of the present invention is shown. The multi-domain vertical alignment LCD200includes a first substrate210, a second substrate220parallel to the first substrate210, and a liquid crystal layer230sandwiched therebetween. The liquid crystal layer230includes a number of liquid crystal molecules (not labeled) having negative dielectric anisotropy.

The first substrate210includes an upper polarizer212, a first transparent substrate211, a color filter213, a common electrode215, and a first alignment film214arranged in that order from top to bottom. The first substrate210further includes a number of first protrusions241, a number of second protrusions242, a number of third protrusions243, and a number of fourth protrusions244. The first, second, third, and fourth protrusions241,242,243,244are arranged at an inner surface of the common electrode215. The color filter213includes a number of red filters, a number of green filters, and a number of blue filters sequentially arranged in that order.

The second substrate220includes a second transparent substrate221and a lower polarizer222formed at an outside surface of the second transparent substrate221. The second substrate220further includes a number of data lines223, a number of gate lines225, and a number of pixel electrodes227formed at an inner surface of the second transparent substrate221, and a second alignment film224formed at an inner surface of the pixel electrode227. The data lines223are parallel to each other, with each of the data lines223extending along a first direction. The gate lines225are parallel to each other, with each of the gate lines225extending along a second direction that is orthogonal to the first direction. A smallest area formed by any two adjacent gate lines225together with any two adjacent data lines223defines a pixel region229thereat.

In each pixel region229, the second substrate220further includes a number of first slits281, a number of second slits282, a number of third slits283, a number of fourth slits284defined in the pixel electrodes227.

Each pixel region229corresponds to a red filter, a green filter or a blue filter of the color filter213, and includes a first sub-pixel region250and a second sub-pixel region260.

Each first sub-pixel region250corresponds to two of the first protrusions241, one of the second protrusions242, one of the first slits281, and two of the second slits282. The first protrusions241and the second protrusions242have triangular transverse sectional shapes.

Each first protrusion241includes a first main strip241aand a first extending strip241bconnecting to the first main strip241a. In each first sub-pixel region250, the two first main strips241aof the first protrusions241are arranged along a substantially V-shaped path. Each first main strip241ais arranged along a respective one of the two arms of the V-shaped path. The two first extending strips241bextend from two ends of the two first main strips241arespectively, and are parallel to the gate lines225. As illustrated, the two first extending strips241bextend to two right-side corners of the first sub-pixel region250, as viewed inFIG. 1. The two first protrusions241in each first sub-pixel region250are symmetrical about an axis251. In the illustrated embodiment, an angle formed between the two first main strips241ais approximately 90°.

The second protrusion242is arranged along a substantially T-shaped path, which is located in a space between the two first protrusions241. The second protrusion242includes two inclined sides242a, at two inner elbow portions of the T-shaped path. The inclined sides242aare parallel to the first main strips241a, respectively. The second protrusion242is symmetrical about the axis251.

The first slit281is arranged along a Y-shaped path, and is located between the main strips241aand the second protrusion242as viewed inFIG. 1. The first slit281includes a V-shaped slit281aadjacent the second protrusion242, and a strip slit281bconnecting to a point portion of the V-shaped slit281a. The strip slit281bis arranged along the axis251, and is adjacent to where the first main strips241aoppose each other. The V-shaped first slit281aare parallel to the V-shape formed by the first main strips241a.

The second slits282in the first sub-pixel region250are each arranged along a strip path, and are parallel to the first main strips241a, respectively. The second slits282are located at two left corners of the first sub-pixel region250, as viewed inFIG. 1. The first main strips241a are located between the first slit281and the second slits282, respectively, in each first sub-pixel region250.

A horizontal distance W1between the V-shaped slit281aof the first slit281and either one of the adjacent second slits282is defined as a first width of the pixel electrode227in each first sub-pixel region250. The distance W1is calculated such that portions of the second alignment film224at the first slit281and either one of the adjacent second slits282are not included in the span of the distance W1. A width of the first slit281and either one of the second slits282is defined as L1. The width L1is calculated such that portions of the second alignment film224at the first slit281and either one of the second slits282are included in the span of the width L1.

The second sub-pixel region260is similar to the first sub-pixel region250. The second sub-pixel region202corresponds to two of the third protrusions243, one of the fourth protrusions244, one of the third slits283, and two of the fourth slits284. The third protrusions243, the fourth protrusion244, the third slit283, and the fourth slits284of the second sub-pixel region260are similar to the first protrusions241, the second protrusion242, the first slit281, and the second slits282of the first sub-pixel region250, respectively. However, each third protrusion243further includes a second extending strip243c. The two second extending strips243cextend from two ends of two third main strips (not labeled) of the two third protrusions243. The two second extending strips243cextend toward each other, and are adjacent and parallel to the corresponding data line223. The two second extending strips243care symmetrical about an axis (not labeled) of the second sub-pixel region260, such axis being similar to the axis251of the first sub-pixel region250.

In the illustrated embodiment, one of the first extending strips241bof the first sub-pixel region250adjacent to the second sub-pixel region260is a “shared” first extending strip241b, because it also constitutes one of the first extending strips (not labeled) of the second sub-pixel region260adjacent to the first sub-pixel region250.

A horizontal distance W2between the third slit283and either one of the adjacent fourth slits284is defined as a second width of the pixel electrode227in each second sub-pixel region260. The distance W2is calculated such that portions of the second alignment film224at third slit283and either one of the adjacent the fourth slit284are not included in the span of the distance W2. A width of the third slit283and either one of the fourth slits284is defined as L2. The width L2is calculated such that portions of the second alignment film224at the third slit283and either one of the fourth slits284are included in the span of the width L2. The second width W2is greater than the first width W1, and the width L2is approximately equal to the width L1.

According to the above-described configuration, the first sub-pixel region250is divided into four domains A, B, C, D, by the first and second protrusions241,242and the first and second slits281,282. The second sub-pixel region260is divided into four domains E, F, G, H, by the third and fourth protrusions243,244and the third and fourth slits283,284.

When the multi-domain vertical alignment LCD200is in an on state, voltages are applied thereto. In the first sub-pixel region250, a voltage difference between the common electrode215and pixel electrodes227generates a fringe electric field. The fringe electric field is inclined near the first slit281and the second slit282. Because the liquid crystal molecules have negative dielectric anisotropy, they are inclined to orient perpendicular to the direction of the fringe electric field. Considering the effects of the first protrusions241and the second protrusions242together, the liquid crystal molecules are oriented at an angle θ1with respect to the second substrate220, and are oriented in four directions a, b, c, d in the four domains A, B, C, D, respectively.

Liquid crystal molecules in the second sub-pixel region260are oriented in four directions e, f, g, h in similar fashion to the liquid crystal molecules of the first sub-pixel region250. However, because the width W1between the first and second slits281is less than the width W2between the third and fourth slits283,284, strengths of fringe fields in the first sub-pixel region250are less those of the second sub-pixel region260. Thus, the liquid crystal molecules are oriented at an angle θ2with respect to the second substrate220. The angle θ2of the liquid crystal molecules in the second pixel region260is less than the angle θ1of the liquid crystal molecules in the first pixel region250.

In a word, strengths of fringe fields in the two sub-pixel regions250,260are different from each other when any one voltage is applied to the multi-domain vertical alignment LCD200. Thus angles between the liquid crystal molecules and the second substrate220in the two sub-pixel regions250,260are different from each other under any one applied voltage. Therefore, the multi-domain vertical alignment LCD200is an eight-domain vertical alignment LCD.

Unlike conventional multi-domain LCDs, the multi-domain vertical alignment LCD200attains a visual effect that is an overall result of eight domains, and therefore provides a very even display performance. Thus, a display quality of the multi-domain vertical alignment LCD200is improved.

Furthermore, portions of the first, second, third, and fourth protrusions241,242,243,244parallel to the gate line225and data line223can prevent liquid crystal molecules located at borders between two adjacent domains from having no on-state orientation.

Referring toFIG. 3, a multi-domain vertical alignment LCD300according to a second embodiment of the present invention is shown. The multi-domain vertical alignment LCD300is similar to the multi-domain vertical alignment LCD200. However, a common electrode315thereof defines a number of fifth slits (not labeled), which respectively replace the first, second, third, and fourth protrusions241,242,243,244of the multi-domain vertical alignment LCD200. The fifth slits are arranged similar to the first, second, third, and fourth protrusions241,242,243,244of the multi-domain vertical alignment LCD200.

Further or alternative embodiments may include the following. In a first example, the first, second, third, and fourth slits281,282,283,284can be replaced by a number of protrusions arranged similar to the first, second, third and fourth slits281,282,283,284. In a second example, the width L1of each first slit281can be different from the width L2of each third slit283, in order to further differentiate a first ratio W1/L1and a second ratio W2/L2. In a third example, the first protrusions241can be arranged approximately parallel to, or inclined to, the third protrusions243. In a fourth example, the two first main strips241aof the two protrusions241in each first pixel region250connect with each other. In a fifth example, the second extending strips243cof the third protrusions243in each second pixel region260connect with each other.