Liquid-crystal display device

A liquid-crystal display device includes a thin-film transistor (“TFT”) array flat substrate, an opposing flat substrate, a liquid-crystal layer including liquid-crystal molecules having negative dielectric anisotropy between the TFT array flat substrate and the opposing flat substrate, a pattern electrode between the TFT array flat substrate and the liquid-crystal layer, a first liquid-crystal alignment layer including an electric field sensitive polymer compound between the pattern electrode and the liquid-crystal layer, a patternless electrode between the opposing flat substrate and the liquid-crystal layer and a second liquid-crystal alignment layer between the patternless electrode and the liquid-crystal layer where the electric field sensitive polymer includes a main chain, vertically-aligned side chains, and liquid-crystalline side chains including a mesogen unit having at least two cyclic combinations, a polar group coupled with an end of the mesogen unit, and a flexible group coupled with another end of the mesogen unit.

This application claims priority to Korean Patent Application No. 10-2016-0006281, filed on Jan. 19, 2016, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference.

BACKGROUND

Exemplary embodiments of the invention relate to a liquid-crystal display (“LCD”) device.

2. Description of the Related Art

A display device is an output device which presents data in a form of images. As the information-oriented society evolves, various demands for display devices are ever increasing. Among various types of display devices, flat panel display devices such as a flat liquid-crystal display (“LCD”) device, a flat plasma display panel (“PDP”) device, and a flat organic light-emitting diode display (“OLED”) device are commonly used.

Recently, a flat LCD device is one of the most widely used flat display devices. A flat LCD device may include flat display substrates facing each other and a liquid-crystal layer interposed therebetween.

As recent flat LCD devices have large screens, there is a difference between viewing angles when a viewer watches a center of the large screen and when the viewer watches a right or left end of the large screen. Accordingly, a research is on going into a curved LCD device for compensating such difference in viewing angle.

The curved LCD device may be fabricated by bending a flat LCD device. From a viewer's perspective, the curved LCD devices may be classified as a portrait type curved LCD device having its height larger than its width and bent in a vertical direction, and a landscape type curved LCD device having its width larger than its height and bent in a horizontal direction.

SUMMARY

Exemplary embodiments of the invention provide a liquid-crystal display (“LCD”) device with improved response characteristics and light transmittance.

An LCD device includes a thin-film transistor (“TFT”) array flat substrate, an opposing flat substrate facing the TFT array flat substrate, a liquid-crystal layer interposed between the TFT array flat substrate and the opposing flat substrate, a pattern electrode disposed between the TFT array flat substrate and the liquid-crystal layer, a first liquid-crystal alignment layer disposed between the pattern electrode and the liquid-crystal layer, a patternless electrode disposed between the opposing flat substrate and the liquid-crystal layer and a second liquid-crystal alignment layer disposed between the patternless electrode and the liquid-crystal layer. The liquid-crystal layer includes liquid-crystal molecules having negative dielectric anisotropy. The first liquid-crystal alignment layer includes an electric field sensitive polymer compound. The electric field sensitive polymer includes a main chain, vertically-aligned side chains, and liquid-crystalline side chains. The liquid-crystalline side chains includes a mesogen unit having at least two cyclic compounds, a polar group coupled with an end of the mesogen unit, and a flexible group coupled with another end of the mesogen unit.

According to an exemplary embodiment of the invention, an LCD device with improved response characteristics such as a light transmittance may be provided.

DETAILED DESCRIPTION

When a first element is referred to as being “on”, “connected to”, or “coupled to” a second element, the first element can be directly on, directly connected to, or directly coupled to the second element, or one or more intervening elements may be present. In contrast, when a first element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” a second element, there are no intervening elements intentionally provided between the first element and the second element. Like numbers may refer to like elements in this application. The term “and/or” includes any and all combinations of one or more of the associated items.

As used herein, the symbol “CA˜B” denotes that “the carbon number is between A and B.”

Exemplary embodiments of the invention will hereinafter be described with reference to the accompanying drawings.

FIG. 1is a perspective view of a flat liquid-crystal display (“LCD”) device500according to an exemplary embodiment of the invention.

Referring toFIG. 1, the flat LCD device500may include a flat display substrate SUB1, an opposing flat display substrate SUB2spaced apart from the flat display substrate SUB1with a predetermined cell gap therebetween, and a liquid-crystal layer300interposed between the flat display substrate SUB1and the opposing flat display substrate SUB2.

The flat LCD device500includes a display area I and a non-display area II. In the display area I, images are displayed. In the non-display area II surrounding the display area I, no image is displayed.

The liquid-crystal layer300may include liquid-crystal molecules having negative dielectric anisotropy. In the following description, liquid-crystal molecules having negative dielectric anisotropy are referred to as negative liquid-crystal molecules301.

The flat display substrate SUB1may include a plurality of gate lines GL extending in a first direction D1, and a plurality of data lines DL extending in a second direction D2perpendicular to the first direction D1. Although not shown in the drawings, the gate lines GL may be not only disposed in the display area I but also extended to the non-display area II. In addition, a gate pad (not shown) may be disposed in the non-display area II. Further, in the non-display area II, the flat display substrate SUB1may include a gate pad (not shown). The data lines DL may be not only disposed in the display area I but also extended to the non-display area II. In addition, a data pad (not shown) may be disposed in the non-display area II. Further, in the non-display area II, the flat display substrate SUB1may include a data pad (not shown).

In the display area I, a plurality of pixels PX may be defined by the gate lines GL and the data lines DL and may be arranged in a matrix. However, the invention is not limited thereto, and plurality of pixels PX may not be defined by the gate lines GL and the data lines DL. Each of the plurality of pixels PX may include a pixel electrode180. In the display area I, the flat display substrate SUB1may include a plurality of pixels PX arranged in a matrix and pixel electrodes180.

In the non-display area II, a driving part (not shown) for applying a gate driving signal, a data driving signal and the like to each of the pixels PX may be disposed. Further, in the non-display area II, the flat display substrate SUB1may include the driving part (not shown).

The flat display substrate SUB1may include a thin-film transistor array flat substrate (not shown), a pixel electrode (not shown), a first liquid-crystal alignment layer (not shown), and a light-blocking pattern layer (not shown). The opposing flat display substrate SUB2may include a second flat substrate (not shown), a common electrode (not shown), and a second liquid-crystal alignment layer (not shown). Hereinafter, the flat display substrate SUB1, the opposing flat display substrate SUB2, and the liquid-crystal layer300of the flat LCD device500in an initial state where no electric field is applied will be described in detail with reference toFIGS. 1 and 2.

FIG. 2is a cross-sectional view of the flat LCD device500in the initial state where no electric field is applied.

The flat display substrate SUB1may include a thin-film transistor array flat substrate100, a pixel electrode180, a light-blocking pattern layer BM, and a first liquid-crystal alignment layer190. The pixel electrode180may be disposed between the thin-film transistor array substrate100and the liquid-crystal layer300, and between the thin-film transistor array substrate100and the light-blocking pattern layer BM. The first liquid-crystal alignment layer190may be disposed between the pixel electrode180and the liquid-crystal layer300in the display area I and between the light-blocking pattern layer BM and the liquid-crystal layer300in the non-display area II.

The thin-film transistor array substrate100may include a flat substrate110, a thin-film transistor TFT, a color filter layer160and an organic layer170.

In an exemplary embodiment, the flat substrate110is a base substrate of the thin-film transistor array substrate100and may include a transparent insulative substrate such as glass or transparent plastic.

The thin-film transistor TFT is a switching element and may include a gate electrode125, a gate insulative film130, a semiconductor layer140, a source electrode152and a drain electrode155. The gate electrode125functions as the control terminal of the thin-film transistor TFT. The gate electrode125may be disposed on the flat substrate110and includes a conductive material. The gate electrode125may branch off from the gate lines GL. The gate insulative film130may be disposed between the gate electrode125and the semiconductor layer140to insulate one from the other. The gate insulative film130may be provided from the display area I to the non-display area II. The semiconductor layer140functions as a chain layer of the thin-film transistor TFT, and may be disposed on the gate insulation film130. The source electrode152and the drain electrode155may be disposed on the semiconductor layer140spaced apart from each other, and may include a conductive material. The source electrode152functions as an input terminal of the thin-film transistor TFT. The drain electrode155functions as an output terminal of the thin-film transistor TFT. The source electrode152and the drain electrode155may branch off from the data lines DL. Ohmic contact layers (not shown) may be disposed between the source electrode152and the semiconductor layer140and between the drain electrode155and the semiconductor layer140, respectively.

The color filter layer160may be disposed over the switching element TFT and may include an area overlapping the source electrode152and the drain electrode155. The color filter layer160may be provided in every pixel in the display area I, and may include a first color filter160-1and a second color filter160-2. In an exemplary embodiment, the first color filter160-1and the second color filter160-2may produce different colors. In an exemplary embodiment, each of the first color filter160-1and the second color filter160-2may be one of a red color filter R, a green color filter G and a blue color filter B, for example. However, the invention is not limited thereto, and the first color filter160-1and the second color filter160-2may be various other color filters. The first color filter160-1and the second color filter160-2may be disposed alternately.

The organic layer170including an organic material may be disposed on the color filter layer160. The organic layer170may be extended to the non-display area II.

The pixel electrode180including a conductive material may be disposed on the organic layer170in every pixel PX. The pixel electrode180may be electrically connected to the drain electrode155via a contact hole172that penetrates the color filter layer160and the organic film170. In an exemplary embodiment, the pixel electrode180may include indium tin oxide (“ITO”), indium zinc oxide (“IZO”), indium oxide, zinc oxide, tin oxide, gallium oxide, titanium oxide, aluminum, silver, platinum, chrome, molybdenum, tantalum, niobium, zinc, magnesium, and an alloy thereof or a stack of layers thereof, for example.

The pixel electrode180is a pattern electrode having at least one of a protruding pattern and a slit pattern. In an exemplary embodiment, the pixel electrode180may be a pattern electrode in which the slit pattern is defined. The pixel electrode180, along with the common electrode250, may generate electric field so as to control orientations of liquid crystal molecules301in the liquid-crystal layer300interposed therebetween.

The light-blocking pattern layer BM may be disposed on the thin-film transistor array substrate100and the pixel electrode180. The light-blocking pattern layer BM is also commonly referred to as a black matrix. In the display area I, the light-blocking pattern layer BM may overlap the thin-film transistor TFT and the boundary between the first color filter160-1and the second color filter160-2. The light-blocking pattern layer BM may be not only disposed in the display area I but also extended to the non-display area II.

The first liquid-crystal alignment layer190may be disposed on the pixel electrode180and the light-blocking pattern layer BM. The first liquid-crystal alignment layer190may be not only disposed in the display area I but also extended to the non-display area II. A seal line310has a weak adhesion on the first liquid-crystal alignment layer190. Therefore, when the seal line310is disposed on the first liquid-crystal alignment layer190, the flat display substrate SUB1may be separated from the opposing flat display substrate SUB2. Accordingly, it is desired that the first liquid-crystal alignment layer190does not contact the seal line310in the non-display area II. When the LCD device500is designed to have a narrow bezel, however, a portion of the seal line310may be disposed on the first liquid-crystal alignment layer190. The first liquid-crystal alignment layer190will be described in more detail with reference toFIGS. 3 to 5.

The opposing flat display substrate SUB2is opposed to the flat display substrate SUB1and may include an opposing flat substrate210, a common electrode250, and a second liquid-crystal alignment layer270.

In an exemplary embodiment, the opposing flat substrate210is a base substrate of the opposing flat display substrate SUB2and may include a transparent insulative substrate such as glass or transparent plastic.

The common electrode250may be disposed on the opposing flat substrate210. The common electrode250is a patternless electrode with no slit pattern and no protruding pattern. In the flat LCD device500, the pattern electrode is disposed only on the flat display substrate SUB1, and the patternless electrode is disposed on the opposing flat display substrate SUB2, such that the orientation of the liquid-crystal molecules301is controlled by using the pattern electrode. In an exemplary embodiment, the common electrode250may include ITO, IZO, indium oxide, zinc oxide, tin oxide, gallium oxide, titanium oxide, aluminum, silver, platinum, chrome, molybdenum, tantalum, niobium, zinc, magnesium, and an alloy thereof or a stack of layers thereof, for example. The common electrode250may cover the entirety of the display area I. On the entire surface of the display area I, the common electrode250may be disposed across pixels, as a single piece. The common electrode250may be extended to a part of the non-display area II.

The second liquid-crystal alignment layer270may be disposed on the common electrode250. The second liquid-crystal alignment layer270may be not only disposed in the display area I but also extended to the non-display area II. A seal line310has a weak adhesion on the second liquid-crystal alignment layer270. Therefore, when the seal line310is disposed on the second liquid-crystal alignment layer270, the flat display substrate SUB1may be separated from the opposing flat display substrate SUB2. Accordingly, it is desired that the second liquid-crystal alignment layer270does not contact the seal line310in the non-display area II. When the LCD device500is designed to have a narrow bezel, however, a portion of the seal line310may be disposed on the second liquid-crystal alignment layer270. The second liquid-crystal alignment layer270will be described in more detail with reference toFIGS. 3 to 5.

The flat display substrate SUB1and the opposing flat display substrate SUB2may be coupled together with the seal line310including sealant or the like. The seal line310may be located in the non-display area II. The seal line310is provided along the edge of the display area I to surround the display area I. In the non-display area II, it is desired that the first and second liquid-crystal alignment layers190and270are disposed inner side of the seal line310. When the LCD device500is designed to have a narrow bezel, however, ends of the first and second liquid-crystal alignment layers190and270may partially overlap the seal line310.

In the initial state where no electric field is applied to the flat LCD device500, the negative liquid-crystal molecules301may be oriented substantially vertically with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2. As used herein, the expression “the negative liquid-crystal molecules301are oriented substantially vertically with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2” is intended to indicate that “the negative liquid-crystal molecules301are oriented with a pretilt angle from about 88° to about 90° with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2.” The pretilt angle refers to an angle between the flat display substrate SUB1and directors of the negative liquid-crystal molecules301and an angle between the opposing flat display substrate SUB2and the directors of the negative liquid-crystal molecules301.

FIG. 3Ais an enlarged view of area X of the flat LCD device500shown inFIG. 2, andFIGS. 3B and 3Care enlarged views of areas Y and Z ofFIG. 3A, respectively.FIG. 4is a view showing the behavior of the negative liquid-crystal molecules301in fringe field area A and vertical field area B immediately after electric field is applied to the flat LCD device500shown inFIG. 2.FIG. 5is a view showing the behavior of the negative liquid-crystal molecules301in fringe field area A and vertical field area B in the final state after electric field is applied to the flat LCD device500shown inFIG. 2.

Referring toFIGS. 3A and 3B, in area Y, the first liquid-crystal alignment layer190may include a first electric field sensitive polymer compound including a main chain MC, vertically-aligned side chains VA and positive liquid-crystalline side chains PT1having a polar group. Herein, the first liquid-crystal alignment layer190may be defined as a first electric field sensitive liquid-crystal alignment layer.

The first electric field sensitive polymer compound may be a polyimide-based polymer compound in which a main chain MC includes an imide group in a repeat unit and which includes vertically-aligned side chains VA and positive liquid-crystalline side chains PT1. The vertically-aligned side chains VA and the positive liquid-crystalline side chains PT1may be chemically bonded to the main chain MC via the respective spacer groups SP.

In an exemplary embodiment, the vertically-aligned side chains VA may be a C1-8alkyl group, a hydrocarbon derivative having a terminal substituted with a C1-8alkyl group, a hydrocarbon derivative having a terminal substituted with a C3-6cycloalkyl group, a hydrocarbon derivative having a terminal substituted with an aromatic hydrocarbon, etc., for example. Referring toFIGS. 2 and 3, in the initial state where no electric field is applied to the flat LCD device500shown inFIG. 2, the vertically-aligned side chains VA may align the negative liquid-crystal molecules301substantially vertically with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2.

In an exemplary embodiment, the vertically-aligned side chains VA may be a compound expressed in Chemical Formula 1 below, for example:

When electric field is applied to the flat LCD device500shown inFIG. 2, the positive liquid-crystalline side chains PT1have their major axis aligned along the electric field direction in the fringe field area A, and the dielectric constant of the major axis is larger than that of the minor axis. The positive liquid-crystalline side chains may electrostatically react with the negative liquid-crystal molecules301, so that the positive liquid-crystalline side chains may pretilt the negative liquid-crystal molecules301in the fringe field area A.

The positive liquid-crystalline side chains PT1may include a mesogen structure for exhibiting liquid crystalline property, a polar group coupled with an end of the mesogen structure, and a flexible group coupled with the other end of the mesogen structure. The mesogen structure has affinity for the negative liquid-crystal molecules301and includes at least two cyclic compounds. In an exemplary embodiment, the at least two cyclic compounds may be, for example, a bicyclohexyl group, a cyclohexyl-phenyl group, a biphenyl group, a terphenly group, naphthalene, for example. In an exemplary embodiment, the polar group may enhance alignment control over the negative liquid-crystal molecules301and may be at least one of fluorine group (—F) and cyanogens group (—CN), for example. In an exemplary embodiment, the flexible group may be, for example, C1-8alkyl group or C1-8alkoxy group.

In an exemplary embodiment, the positive liquid-crystalline side chains PT1may be a compound expressed in Chemical Formula 2 below, for example:

In an exemplary embodiment, the content ratio between the vertically-aligned side chains VA and the positive liquid-crystalline side chains PT1may range from 50:50 to 95:5, preferably from 50:50 to 70:30, for example.

Referring toFIG. 4, immediately after electric field e is applied to the LCD device500shown inFIG. 2, in the fringe field area A, some of the negative liquid-crystal molecules301may electrostatically react with the positive liquid-crystalline side chains PT1such that the major axis may be substantially perpendicular to the electric field e. In the vertical field area B where anchoring energy is weak, the negative liquid-crystal molecules301may be randomly oriented with no directivity.

Referring toFIG. 5, however, in the final state after the electric field e is applied to the LCD device500shown inFIG. 2, the directors of the negative liquid-crystal molecules301in the fringe field area A propagates quickly to the vertical field area B as indicated by the arrow, such that in both of the fringe field area A and the vertical field area B, the major axis of the negative liquid-crystal molecules301may be substantially perpendicular to the electric field e.

Referring back toFIGS. 3A and 3C, in area Z, the second liquid-crystal alignment layer270may include the first electric field sensitive polymer compound. Herein, the second liquid-crystal alignment layer270may be defined as a first electric field sensitive liquid-crystal alignment layer.

Although not shown in the drawings, the second liquid-crystal alignment layer270may include a vertically-aligned polymer compound that does not include the positive liquid-crystalline side chains PT1and includes the main chain MC and the vertically-aligned side chains VA. In that case, the second liquid-crystal alignment layer270may be defined as a vertically-aligned liquid-crystal alignment layer. In an exemplary embodiment, the vertically-aligned polymer compound may be a polyimide-based polymer compound in which the main chain includes an imide group in a repeat unit and which is composed only of the vertically-aligned side chains, for example.

FIG. 6is a cross-sectional view of the flat LCD device500shown inFIG. 2in the final state after electric field is applied thereto.FIG. 7is a plan view of a part of a pixel electrode180of the flat LCD device500shown inFIG. 6.FIG. 8is a plan view of a pixel of the flat LCD device500shown inFIG. 6.

Referring toFIGS. 2 and 6, in the initial state where no electric field is applied to the flat LCD device500, the negative liquid-crystal molecules310are oriented substantially vertically with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2. In contrast, in the final state where electric field is applied to the flat LCD device500, the negative liquid-crystal molecules310may be inclined at a pretilt angle with respect to the direction vertical to the flat display substrate SUB1and the opposing flat display substrate SUB2.

Referring toFIG. 7, for example, the pixel electrode180may include a plurality of unit electrodes UP. Each of the unit electrodes UP may be a slit pattern electrode including a cross-like stem SC, minute branches BC extending from the cross-like stem SC where slits DC are defined between the minute braches BC. Specifically, the cross-like stem SC may have a cross+shape with horizontal stems SC1and vertical stems SC2intersecting one another. In an exemplary embodiment, the minute branches BC may extend radially from the cross-like stem SC at approximately 45°, for example. In an exemplary embodiment, the slits DC may extend radially from the cross-like stem SC at approximately 45°, for example. In an exemplary embodiment, the negative liquid-crystal molecules301may extend radially from the cross-like stem SC at approximately 45° along the slits DC, for example.

The pixel electrode180may further include links LK connecting the cross-like stems SC of the unit electrodes UP arranged roughly in a matrix with one another. Horizontal gaps G1and vertical gaps G2may exist between the unit electrodes UP arranged roughly in a matrix.

Referring toFIG. 8, a pixel electrode180may be disposed on a pixel area defined by gate lines GL extending in a first direction D1and data lines DL extending in a second direction D2perpendicular to the first direction D1. The pixel electrode180may include a first sub-pixel electrode180aand a second sub-pixel electrode180b. In an exemplary embodiment, the first sub-pixel electrode180amay include four unit electrodes, for example. In an exemplary embodiment, the second sub-pixel electrode180bmay include six unit electrodes, for example. As such, the first sub-pixel electrode180aand the second sub-pixel electrode180bhave different areas, thereby improving side visibility. However, the invention is not limited thereto, and the first sub-pixel electrode180aand the second sub-pixel electrode180bmay include different numbers of the unit electrodes.

The gate lines GL may include gate electrodes125aand125bprotruding therefrom in the second direction D2toward the pixel electrode180. The data lines DL may include source electrodes152aand152b, and drain electrodes155aand155b. The source electrodes152aand152bmay protrude from the data lines DL and may have a “U” shape. The drain electrodes155aand155bmay be spaced apart from the source electrodes152aand152b. The first sub-pixel electrode180amay be electrically connected to a drain electrode155avia a contact hole172a. The second sub-pixel electrode180bmay be electrically connected to a drain electrode155bvia a contact hole172b.

The reference voltage line178may include horizontal reference voltage lines178aextending in the first direction D1, and vertical reference voltage lines178bextending in the second direction D2and connecting the horizontal reference voltage lines178awith one another to thereby prevent delay in a signal flowing in the reference voltage line178. A lower horizontal reference voltage line178aof the horizontal reference voltage lines178amay overlap a part of the first sub-pixel electrode180abetween the first sub-pixel electrode180aand the gate electrodes125aand125b, and may include a source electrode152cprotruding in the second direction D2from the lower horizontal reference voltage line178atoward the opposite direction of the pixel electrode180. The source electrode152cmay overlap the gate electrode125band may be spaced apart from the drain electrode155c. The drain electrode155cmay be electrically connected to the second sub-pixel electrode180bvia a contact hole172b. An upper reference voltage line178aof the horizontal reference voltage lines178amay be spaced apart from the lower horizontal reference voltage line178b. Unit electrodes of the first sub-pixel electrode180aand the second sub-pixel electrode180bmay be disposed between the upper horizontal reference voltage line178aand the lower horizontal reference voltage line178b.

FIG. 9is an image of an initial behavior of the flat LCD device500shown inFIG. 2.FIG. 10is an image of an initial behavior of a flat LCD device REF according to a comparative example.FIG. 11is an image for comparing a response waveform of the flat LCD device500shown inFIG. 2with a response waveform of the LCD device REF according to the comparative example.

Referring back toFIG. 2, in the flat LCD device500shown inFIG. 2, the liquid-crystal layer300including the negative liquid-crystal molecules301is interposed between the flat display substrate SUB1and the opposing flat display substrate SUB2. Among the electric field generating electrodes, the pixel electrode180is a pattern electrode, and the common electrode250is a patternless electrode. The first liquid-crystal alignment layer190may be the first electric field sensitive liquid-crystal alignment layer. The second liquid-crystal alignment layer270may be the first electric field sensitive liquid-crystal alignment layer or the vertically-aligned liquid-crystal alignment layer.

In contrast, in the flat LCD device REF according to the comparative example, the liquid-crystal layer including the negative liquid-crystal molecules is interposed between the flat display substrate SUB1and the opposing flat display substrate SUB2. All of the electric field generating electrodes are pattern electrodes. All of the liquid-crystal alignment layers are the vertically-aligned liquid-crystal alignment layer. In the following description, the LCD device REF according to the comparative example is also referred to as a patterned vertical alignment mode LCD device.

Referring toFIGS. 9 and 10, it is seen that unlike the flat LCD device REF according to the comparative example, in the flat LCD device500shown inFIG. 2, no texture RT is seen at the ends of the thin-film transistor opening TFTO caused by collision of the orientation of the negative liquid-crystal molecules.

In addition, it is seen fromFIG. 11that the flat LCD device500shown inFIG. 2exhibits the improved response waveform over the LCD device REF according to the comparative example.

FIG. 12is a cross-sectional view of a flat LCD device500-1according to another exemplary embodiment in the initial state where no electric field is applied.FIG. 13Ais an enlarged view of area X′ ofFIG. 12, andFIGS. 13B and 13Care enlarged views of areas Y′ and Z′ ofFIG. 13A, respectively.FIG. 14is a view showing the behavior of the negative liquid-crystal molecules301in fringe field area A and vertical field area B immediately after electric field is applied to the flat LCD device500-1shown inFIG. 12.FIG. 15is a view showing the behavior of the negative liquid-crystal molecules301in fringe field area A and vertical field area B in the final state after electric field is applied to the flat LCD device500-1shown inFIG. 12.

Referring toFIGS. 12 and 13A, in the flat LCD device500-1, the first liquid-crystal alignment layer190′ may include a second electric field sensitive polymer compound including a main chain MC, vertically-aligned side chains VA, and negative liquid-crystalline side chains PT2having polar groups (refer to area Y′ ofFIGS. 13A and 13B). Herein, the first liquid-crystal alignment layer190′ may be defined as a second electric field sensitive liquid-crystal alignment layer.

Referring toFIGS. 2, 3A, 12 and 13A, the first liquid-crystal alignment layer190′ is different from the first liquid-crystal alignment layer190in that the first liquid-crystal alignment layer190′ may include the second electric field sensitive liquid-crystal alignment layer. The first liquid-crystal alignment layer190may be configured as the first electric field sensitive liquid-crystal alignment layer including positive liquid-crystalline side chains PT1.

Referring back toFIGS. 12 and 13A, the second liquid-crystal alignment layer270′ may be the second electric field sensitive liquid-crystal alignment layer. Referring toFIGS. 2, 3A, 12 and 13A, the second liquid-crystal alignment layer270′ is different from the second liquid-crystal alignment layer270in that the second liquid-crystal alignment layer270′ may include the second electric field sensitive liquid-crystal alignment layer. The second liquid-crystal alignment layer270may be configured as the first electric field sensitive liquid-crystal alignment layer including positive liquid-crystalline side chains PT1.

Although not shown in the drawings, the second liquid-crystal alignment layer270′ may include a vertically-aligned polymer compound that does not include the negative liquid-crystalline side chains PT2and includes the main chain MC and the vertically-aligned side chains VA. In that case, the second liquid-crystal alignment layer270′ may be defined as a vertically-aligned liquid-crystal alignment layer. In an exemplary embodiment, the vertically-aligned polymer compound may be a polyimide-based polymer compound in which the main chain includes an imide group in a repeat unit and which is composed only of the vertically-aligned side chains, for example.

When electric field is applied to the flat LCD device500-1, major axis of the negative liquid-crystalline side chains PT2are aligned along the direction perpendicular to the electric field direction in the fringe field area A, and the dielectric constant of the minor axis is larger than that of the major axis. The negative liquid-crystalline side chains may electrostatically react with the liquid-crystal molecules301, so that they may pretilt the liquid-crystal molecules301in the fringe field area A.

The negative liquid-crystalline side chains PT2may include a mesogen structure for exhibiting liquid crystalline property, a polar group coupled with an end of the mesogen structure, and a flexible group coupled with the other end of the mesogen structure. In an exemplary embodiment, the mesogen structure may be a bicyclohexyl group, a cyclohexyl-phenyl group, a biphenyl group, a terphenly group, naphthalene, including at least two cyclic compounds, for example. In an exemplary embodiment, the polar group may be fluorine group (—F), for example. In an exemplary embodiment, the flexible group may be, for example, C1-8alkyl group or C1-8alkoxy group, for example.

In an exemplary embodiment, the negative liquid-crystalline side chains PT2may be a compound expressed in Chemical Formula 3 below, for example:

Referring toFIG. 14, immediately after electric field e is applied to the flat LCD device500-1, in the fringe field area A, some of the negative liquid-crystal molecules301may electrostatically react with the negative liquid-crystalline side chains PT2such that the major axis may be substantially perpendicular to the electric field e. In the vertical field area B where anchoring energy is weak, the negative liquid-crystal molecules301may be randomly oriented with no directivity.

Referring toFIG. 15, however, in the final state after the electric field e is applied to the LCD device500-1, the directors of the negative liquid-crystal molecules301in the fringe field area A propagates quickly to the vertical field area B as indicated by the arrow, such that in both of the fringe field area A and the vertical field area B, the major axis of the negative liquid-crystal molecules301may be substantially perpendicular to the electric field e.

FIG. 16is a view showing a liquid-crystal alignment layer AL including one of the first electric field sensitive polymer compound and the second electric field sensitive polymer compound and the vertically-aligned polymer compound. Herein, the liquid-crystal alignment layer AL including the electric field sensitive polymer compound and the vertically-aligned polymer compound may be defined as a third electric field sensitive liquid-crystal alignment layer. In the liquid-crystal alignment layer AL, the electric field sensitive polymer compound and the vertically-aligned polymer compound are phase-separated, and the polar group has a concentration slope.

Referring toFIGS. 2 and 12, when the liquid-crystal alignment layers190,190′,270and270′ of the flat LCD device500and500-1are configured as the liquid-crystal alignment layer AL, the liquid-crystal alignment layer AL may have a concentration slope of the polar group that is reduced as farther from the liquid-crystal layer300and closer to the electric field generating electrodes180and250. Specifically, when the liquid-crystal alignment layers190,190′,270and270′ of the flat LCD device500and500-1are configured as the liquid-crystal alignment layer AL, at the upper portion U of the liquid-crystal alignment layer AL corresponding to approximately 90% of the thickness of the liquid-crystal alignment layer AL, the concentration of the electric field sensitive polymer compound may be larger than the concentration of the vertically-aligned polymer compound. At the middle portion M of the liquid-crystal alignment layer AL corresponding to approximately 50% of the thickness of the liquid-crystal alignment layer AL, the concentration of the electric field sensitive polymer compound may be substantially equal or similar to the concentration of the vertically-aligned polymer compound. At the lower portion L of the liquid-crystal alignment layer AL corresponding to approximately 20% of the thickness of the liquid-crystal alignment layer AL, the concentration of the vertically-aligned polymer compound may be larger than the concentration of the electric field sensitive polymer compound. Herein, the upper portion U may be defined as an area closer to the liquid-crystal layer300, and the lower portion L may be defined as an area closer to the electric field generating electrodes180and250.

FIG. 17is a perspective view of a curved LCD device500C according to a third exemplary embodiment of the invention.FIG. 18is a cross-sectional view of the curved LCD device500C shown inFIG. 17in the initial state where no electric field is applied thereto.

The curved LCD device500C may be fabricated by bending a flat LCD device. The curved LCD device500C may include a curved display substrate SUB1C, an opposing curved display substrate SUB2C, and a liquid-crystal layer300C interposed therebetween. The thin-film transistor array substrate100C may include a curved substrate110C, a thin-film transistor TFTC, a color filter layer160C and an organic layer170C. The pixel electrode180C including a conductive material may be disposed on the organic layer170C in every pixel PX. The light-blocking pattern layer BMC may be disposed on the thin-film transistor array substrate100C and the pixel electrode180C. The first liquid-crystal alignment layer190C may be disposed on the light-blocking pattern layer BMC and the pixel electrode180C.

The pixel electrode180C is a pattern electrode having at least one of a protruding pattern and a slit pattern. In an exemplary embodiment, the pixel electrode180C may be a pattern electrode in which the slit pattern is defined. The first liquid-crystal alignment layer190C may be one of the first electric field sensitive liquid-crystal alignment layer, the second electric field sensitive liquid-crystal alignment layer, and the third electric field sensitive liquid-crystal alignment layer. The color filter layer160C may include a first color filter160-1C and a second color filter160-2C. A light-blocking pattern layer BMC may be disposed between the color filter layer160C and the first liquid-crystal alignment layer190C and may overlap the thin-film transistor TFTC and the boundary between the first color filter160-1C and the second color filter160-2C.

The opposing curved display substrate SUB2C may include an opposing curved substrate210C, a common electrode250C disposed on the opposing curved display210C, and a second liquid-crystal alignment layer270C disposed on the common electrode250C. The common electrode250C may be a patternless electrode. The second liquid-crystal alignment layer270C may be one of the first electric field sensitive liquid-crystal alignment layer, the second electric field sensitive liquid-crystal alignment layer, the third electric field sensitive liquid-crystal alignment layer, and the vertically-aligned liquid-crystal alignment layer. Considering a machine-hour input to forming films of the liquid-crystal alignment layer190C and270C, in terms of processing efficiency, the first liquid-crystal alignment layer190C and the second liquid-crystal alignment line270C may include the same material.

A surface of the curved LCD device500C facing a viewer may be a concave surface. In an exemplary embodiment, the radius of curvature may range from about 2,000 millimeters (mm) to 5,000 mm, for example. The pretilt angle of the negative liquid-crystal molecules301C at the top point of each of the curved display substrate SUB1C and the opposing curved display substrate SUB2C is substantially equal to the pretilt angle of the negative liquid-crystal molecules301with respect to the flat display substrate SUB1and the opposing flat display substrate SUB2(refer toFIG. 2). Here, the top point refers to a point on a curve where the slope of the tangent line is substantially zero.

FIG. 19shows an alignment state between the upper flat display substrate and the lower flat display substrate in the flat LCD device FLCD according to the comparative example, and an alignment state between the upper curved display substrate and the lower curved display substrate in the curved LCD device CLCD fabricated from the flat LCD device FLCD according to the comparative example.

The flat LCD device FLCD according to the comparative example may be the patterned vertical alignment mode LCD device. During the process of bending the patterned vertical alignment mode LCD device, stress is exerted on the upper and lower flat display substrates, such that the upper flat display substrate may be shifted to the right or to the left relative to the lower flat display substrate, for example. As a result, misalignment may exist between the upper and lower curved display substrates of the curved LCD device CLCD.

Accordingly, when the curved LCD device CLCD is fabricated by bending the patterned vertical alignment mode LCD device, the layout between the upper curved display substrate and the lower curved display substrate may differ from the designed layout between the upper flat display substrate and the lower flat display substrate in the patterned vertical alignment mode LCD device.

The misalignment between the upper curved display substrate and the lower curved display substrate results in the misalignment (indicated by the dotted rectangular) at the boundary between the domains, and the misalignment at the boundary of the domains results in the interference or collision of the orientation of the liquid-crystal molecules having the negative dielectric anisotropy. Accordingly, the liquid-crystal molecules having the negative dielectric anisotropy located between the liquid-crystal molecules having the negative dielectric anisotropy oriented on the surface of the liquid-crystal alignment layer may be oriented substantially vertically. As a result, in the curved LCD device CLCD, texture may be perceived in the area indicated by the dotted rectangular as a spot or a dark portion, such that light transmittance of the curved LCD device CLCD may be lowered.

Referring back toFIG. 18, in the curved LCD device500C, only the pixel electrode180C is configured as a pattern electrode while the common electrode250C is configured as a patternless electrode. Accordingly, the orientation of the negative liquid-crystal molecules301C is controlled by using the pixel electrode180C, and thus it is possible to prevent texture due to the misalignment between the curved display substrate SUB1C and the opposing curved display substrate SUB2C. As a result, the curved LCD device500C may exhibit improved light transmittance over the curved LCD device CLCD fabricated from the flat LCD device FLCD according to the comparative example (refer toFIG. 19).

In addition, referring toFIG. 18, in the curved LCD device500C, the first liquid-crystal alignment layer190C includes one of the first electric field sensitive liquid-crystal alignment layer, the second electric field sensitive liquid-crystal alignment layer, and the third electric field sensitive liquid-crystal alignment layer. Accordingly, the curved LCD device500C may exhibit improved response characteristics over the curved LCD display device CLCD according to the comparative example (refer toFIG. 19).

In addition, referring toFIG. 18, in the curved LCD device500C, the curved display substrate SUB1C includes the color filter layer160C, and thus it is possible to prevent color mixing due to the misalignment between the curved display substrate SUB1C and the opposing curved display substrate SUB2C. In addition, since the curved display substrate SUB1C includes the light-blocking pattern layer BMC, it is possible to prevent decrease in light transmittance due to the misalignment of the light-blocking pattern layer BMC resulted from the misalignment between the curved display substrate SUB1C and the opposing curved display substrate SUB2C. The gate electrode125C, gate insulation film130C, the semiconductor layer140C, the source electrode152C, the drain electrode155C and the seal line seal line310C may be substantially similar to the gate electrode125, gate insulation film130, the semiconductor layer140, the source electrode152, the drain electrode155and seal line310shown inFIG. 2, and thereby the detailed descriptions will be omitted.

It will be apparent to those skilled in the art that various modifications and variation may be made in the described embodiments. The described embodiments cover modifications and variations within the scope defined by the appended claims and their equivalents.