Liquid crystal display device

The present invention discloses a liquid crystal display (LCD) device. The LCD device comprises an upper substrate and a lower substrate. Every two data lines and two scan lines define two pixels. Each pixel comprises a pixel electrode and a transistor, and a biased electrode is arranged under a slot between two pixel electrodes of the two pixels. When positive frame, the voltage of the biased electrode, VE, is greater than the voltage the pixel electrode, VP; when negative frame, the voltage of the biased electrode, VE, is smaller than the voltage the pixel electrode, VP.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device that comprises pixels having novel structures.

2. Description of the Prior Art

Many liquid crystal displays, such as Multi-domain vertical alignment type liquid crystal display, bear a high contrast ratio, fast response time, and a wide viewing angle by applying an electric field to reorient liquid crystal molecules in the displays.

FIG. 1is a cross sectional view of a vertical alignment type liquid crystal display according to prior art. In order to alter alignment of liquid crystals12, a pixel electrode4is formed on a lower substrate2and a plurality of protrusions6are formed at the pixel electrode4. In addition, a common electrode10is formed below an upper substrate14and a plurality of protrusions8are formed below the common electrode10. The structure mentioned above results in the liquid crystals12tilting a little bit due to the presence of the protrusions6,8. When voltages are applied to the pixel electrode4and the common electrode10, a transverse-electric field is generated as the dotted-line arrows to reorient liquid crystal molecules12in different angles and thus increase the transmittance.

FIG. 2shows a cross sectional view of another vertical alignment type liquid crystal display according to prior art. The structure of which is similar to the structure shown inFIG. 1, the difference is that a plurality of openings16formed by an etching process to replace the protrusions6. Also, when voltages are applied to the pixel electrode4and the common electrode10, a transverse-electric field is generated as the dotted-line arrows to reorient liquid crystal molecules12in different angles and thus increase the transmittance.

In addition, the liquid crystal display comprises a plurality of scan lines and data lines constructing driving circuits, where the data lines are connected to the data drivers, and the scan lines are connected to the scan drivers. Because the resolution of the liquid crystal display is increased, the number of the scan lines and data lines will be inevitably increased, and the cost is also increased. For lowering the cost, the number of the data lines must be decreased.

FIG. 3shows the structure of the pixels of a conventional liquid crystal display. For simplicity and convenience, only the lower substrate, the substrate for producing transistors thereon, a partial plan view of which is shown. As shown inFIG. 3, in each row of pixel electrode P0-P4, two pixel electrodes across the data line are driven by the same data line, and driven by two different scan lines individually. For example, data line S2drives both of pixel electrode P1and pixel electrode P2, scan line G1drives pixel electrode P1but scan line G2drives pixel electrode P2; data line S3drives both of pixel electrode P3and pixel electrode P4, scan line G1drives pixel electrode P3but scan line G2drives pixel electrode P4. The structure shown inFIG. 3can decrease the number of data lines.

A Taiwan Patent, issued number 548615, entitled “Display device having three adjacent pixel electrodes driven by the same data line,” disclose a display device having three adjacent pixel electrodes are selectively driven by the same data line via a first switch, a second switch, and a third switch. The number of data lines can be further decreased.

In each row of pixel electrodes, every two or three pixel electrodes are driven by the same data line as mentioned above has been applied in liquid crystal display devices such as the vertical alignment type as mentioned above. However, some difficulties are encountered. The major difficulty is the arrangement between two adjacent pixel electrodes. The arrangement must consider the fringe field and crosstalk between pixel electrodes. For generating larger pretilt angles, the fringe field should be large enough; for smaller crosstalk, the distance between two pixel electrodes should be increased. However, increasing the distance between two pixel electrodes will lower the aperture ratio. Besides, the fringe field is not large enough and the crosstalk is still troublesome.

Therefore, it would be advantageous to provide a novel liquid crystal display device having novel structure of pixels, especially for every two or three pixel electrodes driven by the same data line, to overcome the defects of the prior art.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a liquid crystal display device that can increase the fringe field, reduce the crosstalk, enhance the aperture ratio, and reduce the response time.

According to the object, the present invention provides a liquid crystal display device, which comprises an upper substrate, and a lower substrate. Where the lower substrate comprises a plurality of data lines and a plurality of scan lines perpendicular to one another to construct an array of pixel, each two data lines and two scan lines define two pixels, each pixel comprises a pixel electrode and a transistor, and a biased electrode is arranged below a slot between the two pixel electrodes of the two pixels, and where the biased electrode has a voltage VE, and the two pixel electrodes have a voltage VP, when one or two of the two pixel are in the positive frame, VP>VE, when one or two of the two pixels are in the negative frame, VP<VE.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description of the present invention will be discussed in the following embodiments, which are not intended to limit the scope of the present invention, but can be adapted for other applications. While drawings are illustrated in details, it is appreciated that the quantity of the disclosed components may be greater or less than that disclosed, except expressly restricting the amount of the components. Wherever possible, the same or similar reference numbers are used in drawings and the description to refer to the same or like parts. It should be noted that any drawings presented are in simplified form and are not to precise scale. In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms, such as, top, bottom, left, right, up, down, over, above, below, beneath, rear, and front, are used with respect to the accompanying drawing. Such directional terms should not be construed to limit the scope of the invention in any manner.

FIG. 4shows a structure of pixels of a vertical-alignment type liquid crystal display device according to one embodiment of the present invention. The structure of pixels comprises an upper substrate for producing color filters thereon and a lower substrate30for producing transistors thereon. For simplicity and convenience,FIG. 4only shows a partial plan view of the lower substrate30. The lower substrate30comprises a plurality of data lines such as S1-S3and a plurality of scan lines G0-G5, which are perpendicular to one another. Each two data lines and two scan lines define two pixels. Each pixel comprises a pixel electrode such as P1-P8and a transistor such as T0-T8. Each transistor comprises a gate, a source, and a drain, where the drain coupled to the pixel electrode, the gate coupled to a scan line, and the source coupled to a data line. In each row of pixel electrodes (P0-P4, P5-P8), every two of the pixel electrodes are driven by the same data line, and driven by two different scan lines. For example, data line S2drives both of pixel electrode P1and pixel electrode P2, scan line G1drives pixel electrode P1but scan line G2drives pixel electrode P2; data line S3drives both of pixel electrode P3and pixel electrode P4, scan line G1drives pixel electrode P3but scan line G2drives pixel electrode P4. In addition, a biased electrode (for example, E1-E2) is formed below a slot between the two pixel electrodes of two pixels defined by every two neighboring data lines and every two neighboring scan lines. The biased electrodes E1-E2will be helpful to realize the object of the invention.

It is appreciated that the position of the transistors T0-T8are not restricted according to the present invention. The position of the transistors T0-T8may be changed to comply with various drive methods including row inversion, dot inversion, column inversion, frame inversion, and so forth. For example, the transistor T6connected to data line S2and scan line G3may be changed to connect data line S2and scan line G4; the transistor T5connected to data line S1and scan line G4may be changed to connect data line S1and scan line G3. Further, the biased electrodes E1-E2may be applied to a vertical-alignment type liquid crystal display device that every three or more pixel electrodes are driven by the same data line in each row of pixel electrodes.

FIG. 5is a cross sectional view taken along line A-A′ inFIG. 4according to one embodiment of the present invention; besides, this drawing further shows the detail of the upper substrate32. A color filter34is formed below the upper substrate32. The color filter34comprises a plurality of color resists36having different color constructing an array, and each two color resists36are separated by a black matrix B1-B3. A common electrode38is formed below the color filter34. Each color resist orientates a pixel electrode P7-P8of the lower substrate30; each black matrix B1-B3orientates a data line S2-S3or a biased electrode E2. The biased electrode E2is formed below a slot C2between two pixel electrodes P7-P8.

As shown inFIG. 5, the width of the biased electrode E2is larger than the width of the slot C2, and the width of the black matrix B2is larger than the width of the biased electrode E2. In other embodiments, the width of the biased electrode E2may equal the width of the slot C2, and the width of the black matrix B2may equal the width of the biased E2, the later circumstance having been shown inFIG. 6.FIG. 6differs fromFIG. 5only in the width of the black matrix B2and the biased electrode E2. Notice that the width of the black matrix B2may be different from the width of the black matrix B1or the black matrix B3. In addition, both of the biased electrode E2and the data lines S2-S3are formed at the same layer; that is, the biased electrode E2and the data lines S2-S3may be formed in the same procedure and formed by the same material. Further, some elements are not shown in this drawing for simplicity. These elements comprises a gate formed on the lower substrate30, a insulating layer formed on the gate, a source, a drain, and a data line formed at the same layer on the insulating layer; a protecting layer formed on the source, drain, and data line; a liquid crystal layer formed between the upper substrate32and the lower substrate30; and two alignment layer for aligning the liquid crystal layer respectively formed below the common electrode38and formed on the pixel electrodes P7-P8.

Because the biased electrode E2also can shield light, the black matrix B2is omitted in another embodiment, as shown inFIG. 7; there has no black matrix arranged above the biased electrode E2.

According to the present invention, a voltage VEis applied to the biased electrode E2and the common electrode38, and a voltage VPis applied to the pixel electrodes P7-P8. The experiment results show that the absolute value of VPshould be greater than the absolute value of VEfor enhancing the fringe field between the pixel electrodes P7-P8. That is, when positive frame voltage VPand VEis applied (when current pixel is in the positive frame), VP>VE, when negative frame voltage VPand VEis applied (when current pixel is in the negative frame), VP<VE.

The key feature of the present invention comprises a biased electrode arranged below a slot between two pixel electrodes. Other features disclosed by the prior art may be added to the present invention to enhance the transverse-electric field of the vertical-alignment type liquid crystal display device.FIG. 8shows another embodiment according to the present invention.FIG. 8differs fromFIG. 7in that a plurality of protrusions40are formed below the common electrode38(or above the alignment layer) for increasing the pretilt angle of the liquid crystals. In other embodiments, the common electrode38may comprise a plurality of openings instead of the plurality of protrusions40shown inFIG. 8. Similarly, the pixel electrodes P7-P8may comprise a plurality of protrusions or a plurality of openings for enhancing the transverse-electric field.FIG. 9shows another embodiment according to the present invention.FIG. 9differs fromFIG. 8in which a shielding electrode42is arranged below and arranged adjacent to the data lines S2-S3for reducing the crosstalk between the pixel electrodes P7, P8and the data lines S2, S3. The shielding electrode42and the scan lines may be formed at the same layer. Notice that the features disclosed inFIG. 8andFIG. 9may be applied to any embodiments of the present invention.

FIGS. 10-13show some embodiments of the present invention, where the same or similar reference numbers are used in drawings and the description to refer to the same or like parts. Referring toFIG. 10, the length of the biased electrodes E1-E4approximates the length of the slot between pixel electrodes P0-P8and the biased electrodes E1-E4is within each of the pixels. In this embodiment, the biased electrodes E1-E4, the scan lines G0-G5, and the gates are formed at the same layer and below the data lines S1-S3. For supplying voltages to the biased electrodes E1-E4, a latitudinal electrode (not shown) may cross the data lines S1-S3and connects the biased electrodes (E1-E2or E3-E4).

Referring toFIG. 11, the biased electrodes E1-E2and the data lines S1-S3are formed at the same layer. In addition, the biased electrodes E1-E2are extended to cross the scan lines G0-G5. Further, each pixel electrode P0-P8comprise a plurality of openings for enhancing the transverse-electric field. Notice that the number, shape, and position of the opening are not restricted.

Referring toFIG. 12, the biased electrodes E1-E2and the data lines S1-S3are formed at the same layer. In addition, the biased electrodes E1-E2are extended to cross the scan lines G0-G5. Further, each pixel electrode P0-P8comprises a plurality of openings, and the biased electrodes E1-E2are branched to extend below the plurality of openings for enhancing the transverse-electric field and reducing the response time.

Referring toFIG. 13, the length of the biased electrodes E1-E4approximates the length of the slot between pixel electrodes P0-P8and the biased electrodes E1-E4is within each of the pixels. In this embodiment, the biased electrodes E1-E4, the scan lines G0-G5, and the gate (not shown) are formed at the same layer and below the data lines S1-S3. For supplying voltages to the biased electrodes E1-E4, a latitudinal electrode (not shown) may cross the data lines S1-S3and connects the biased electrodes (E1-E2or E3-E4). In addition, each pixel electrode P0-P8comprises a plurality of openings, and the biased electrodes E1-E4are branched to extend below the plurality of openings for enhancing the transverse-electric field and reducing the response time.

The inventive concept of the present invention not only can be applied to vertical-alignment type LCD device, but also can be applied to other types of LCD device.FIGS. 14-15show an exemplary embodiment of a Fringe Field Switching (FFS) type liquid crystal display device according to the present invention.

The embodiment and its variance of the FFS type LCD device are similar to the embodiments of the vertical-alignment type LCD device described above. For simplicity, the same or similar reference numbers are used to refer to the same or like parts, and the description of which are omitted.

The major difference between the FFS type and the vertical-alignment type LCD device is an array common52, made of a material same as the pixel electrodes P0-P8, is formed between the biased electrode E2and the lower substrate30instead of being formed below the color filter34of the upper substrate32. The region that the array common52covered may be larger than or approximate to the region pixel electrodes P7-P8covered. In addition, a color filter over coat50may be formed below the color filter34to protect it. In addition, the biased electrode E2and the scan lines G0-G5are formed in the same layer but they are electrically insulated to each other. Because the biased electrode E2may be extended to cross the scan lines G0-G5, a bridge56is formed over the scan lines G0-G5at the crossing region between the biased electrode E2and the scan lines G0-G5. The bridge56and the date lines S1-S3may be formed at the same layer. A contact hole (not shown) and an electrode (not shown) over the contact hole may be formed later to establish electrical connection between the biased electrode E2and the bridge56. The pixel electrodes P0-P8and the electrode that connects the biased electrode E2and the bridge56may be formed at the same layer. The bridge56straddles the scan lines G0-G5such that the biased electrode E2and the scan lines G0-G5can be electrically insulated with each other.

Notice that a different shape of a plurality of openings54may be formed within each pixel electrode P0-P8, and the number, shape, and position of the opening54may be same as the embodiments illustrated before.

The biased electrode E2has a voltage VE, the array common52has a voltage VC, and the pixel electrodes S2-S3have a voltage VP, where VEequals VC, when VPand VEare in the positive frame, VP>VE, when VPand VEare in the negative frame, VP<VE.

The FFS type LCD device of the present invention has the following advantages: (1) the structure is configured to no extra common lines are needed; (2) the array common can be used for electrical shielding and the biased electrode can be used for black matrix; (3) the FFS type LCD device of the present invention has an excellent aperture ratio comparing to other LCD modes.

According to the present invention, the distance between the two pixel electrodes can be reduced because the biased electrode will provide excellent shielding effect to lower the crosstalk between the two pixel electrodes. In the prior arts, the width of the slot between two adjacent pixel electrodes is about 8 to 10 μm. According to the present invention, the width of the slot between two adjacent pixel electrodes is about 4 to 8 μm. In one embodiment of the present invention, the width of the slot between two adjacent pixel electrodes is 6 μm. In addition, because the voltage of the pixel electrode VPis greater than the voltage of the biased electrode VE, the fringe field between two adjacent pixel electrodes is increased on condition that the original direction of the electric field within the pixel has not been altered. Therefore the response time can be reduced and other related defects such as the touch mura can be improved as well. Moreover, because the distance between two adjacent pixel electrodes is reduced, the area of the black matrix oriented toward the slot between the two adjacent pixel electrodes can be reduced, thus enhancing the aperture ratio.