LIQUID CRYSTAL COMPOSITION AND LIQUID CRYSTAL DISPLAY DEVICE INCLUDING THE SAME

A liquid crystal display device includes: a first substrate including a plurality of pixel areas; a first sub-pixel electrode disposed in a first pixel area on the first substrate; a second sub-pixel electrode disposed in the first pixel area on the first substrate and spaced apart from the first sub-pixel electrode, and a polarity of a voltage applied to the second sub-pixel electrode with reference to a common voltage is different from a polarity of a voltage applied to the first sub-pixel electrode with reference to the common voltage; a second substrate facing the first substrate and spaced apart from the first substrate; and a liquid crystal layer which interposed between the first substrate and the second substrate and including a liquid crystal composition having dielectric anisotropy of about −2.5 to about −1.5.

This application claims priority to Korean Patent Application No. 10-2015-0132026, filed on Sep. 18, 2015, 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 OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal composition and a liquid crystal display device including the same.

2. Description of the Related Art

A liquid crystal display device is one type of widely used flat panel display devices. The liquid crystal display includes two substrates including a field generating electrode, such as a pixel electrode, and a common electrode, and a liquid crystal layer interposed between the two substrates.

The liquid crystal display device applies a voltage to the field generating electrode to generate an electric field in the liquid crystal layer. The electric field determines the orientation direction of the liquid crystals in the liquid crystal layer, and displays an image by controlling the polarization of incident light.

Meanwhile, along with diversification of the application of the liquid crystal display device, it is desirable that the liquid crystal display device possess various characteristics, such as low-voltage drive, high-voltage maintenance ratio, wide viewing angle characteristics, improved contrast, a wide operating temperature range and high-speed response. Attempts have been made to improve the above-mentioned characteristics of the liquid crystal display device, in particular, by controlling the physical properties of the liquid crystal composition included in the liquid crystal layer.

SUMMARY

The liquid crystal molecules used in a liquid crystal display device, in particular, a transverse electric field liquid crystal display device, may have a positive dielectric anisotropy or a negative dielectric anisotropy. When the liquid crystal molecules in the liquid crystal display device have negative dielectric anisotropy, there is an advantage in that transmittance and contrast are higher than a liquid crystal display device including liquid crystal molecules having positive dielectric anisotropy.

Meanwhile, since fluorine substituents contained in the liquid crystal molecules with negative dielectric anisotropy have a high electronegativity, there is an increased attractive force between the liquid crystal molecules which induces a smectic phase capable of easily inducing crystallization of the liquid crystal molecules. Thus, these types of liquid crystal molecules have characteristics in which the viscosity of liquid crystal compositions increase, the response speed is reduced, and the low-temperature margin is disadvantageous.

Thus, an aspect of the present invention provides a liquid crystal composition which has low viscosity and a low low-temperature margin.

Another aspect of the present invention provides a liquid crystal display device which has an improved response speed, a wide operating temperature range, and low power consumption.

Further, still another aspect of the present invention provides a liquid crystal display device in which the transmittance and the contrast are improved, and a display quality is also improved.

According to an exemplary embodiment, there is provided a liquid crystal display device which includes a first substrate having a plurality of pixel areas; a first sub-pixel electrode disposed in a first pixel area on the first substrate; a second sub-pixel electrode disposed in the first pixel area on the first substrate and spaced apart from the first sub-pixel electrode, and in which a polarity of a voltage applied to the second sub-pixel electrode with reference to a common voltage is different from a polarity of a voltage applied to the first sub-pixel electrode with reference to the common voltage; a second substrate facing the first substrate and spaced apart from the first substrate; and a liquid crystal layer interposed between the first substrate and the second substrate and including a liquid crystal composition having dielectric anisotropy of about −2.5 to about −1.5.

In an exemplary embodiment, the liquid crystal display device may further include a common electrode disposed on the second substrate and facing the first sub-pixel electrode and the second sub-pixel electrode and to which the common voltage is applied, the liquid crystal layer interposed between the common electrode and the first and second electrode, and an absolute value of the electric field between the first sub-pixel electrode and the common electrode may be the same as an absolute value of the electric field between the second sub-pixel electrode and the common electrode.

In an exemplary embodiment, the liquid crystal display device may further include: at least one first gate line disposed between the first substrate and the first sub-pixel electrode and extending in one direction; at least one second gate line disposed between the first substrate and the first sub-pixel electrode and extending in the one direction; and a plurality of data lines disposed between the first substrate and the first sub-pixel electrode, the plurality of data lines including a first data line, a second data line, and a third data line each intersecting the first gate line and the second gate line, and where the plurality of data lines are electrically insulated.

In an exemplary embodiment, the first sub-pixel electrode may be electrically connected to the first gate line and the first data line, and the second sub-pixel electrode may be electrically connected to the first gate line and the second data line.

In an exemplary embodiment, the polarity of the voltage applied to the first data line with reference to the common voltage may be different from the polarity of the voltage applied to the second data line with reference to the common voltage, in a single frame interval.

In an exemplary embodiment, the liquid crystal display device may further include: a third sub-pixel electrode disposed in a second pixel area on the first substrate, the second pixel area different from the first pixel area, wherein the third sub-pixel electrode is electrically connected to the second gate line and the second data line.

In an exemplary embodiment, the liquid crystal display device may further include: a fourth sub-pixel electrode disposed in the second pixel area on the first substrate and spaced apart from the third sub-pixel electrode, where a polarity of voltage applied to the fourth sub-pixel electrode is different from a polarity of the voltage applied to the third sub-pixel electrode with respect to the reference voltage, where the fourth sub-pixel electrode may be electrically connected to the second gate line and the third data line.

In an exemplary embodiment, the polarity of the voltage applied to the second data line with reference to the common voltage may be different from the polarity of the voltage applied to the third data line with reference to the common voltage, in a single frame interval.

According to an exemplary embodiment, there is provided a liquid crystal display device which includes: a first substrate including a plurality of pixel areas; a first electrode disposed in a first pixel area on the first substrate; a second substrate facing the first substrate and spaced apart from the first substrate; a second electrode disposed on the second substrate; and a liquid crystal layer interposed between the first substrate and the second substrate and including a liquid crystal composition having dielectric anisotropy of about −2.5 to about −1.5 and refractive index anisotropy of about 0.090 to about 0.120.

In an exemplary embodiment, the liquid crystal display device may have a cell gap in a range of about 2.8 μm to about 3.4 μm.

In an exemplary embodiment, the liquid crystal composition may contain a compound represented by following Chemical Formula 1 in an amount of about 10 weight percent to about 30 weight percent based on an entire weight of the liquid crystal composition.

Where, in chemical formula 1, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms.

In an exemplary embodiment, the liquid crystal composition may further contain a compound represented by the following Chemical Formula 2 in an amount of about 0.01 weight percent to about 10 weight percent based on the entire weight of the liquid crystal composition.

Where, in Chemical Formula 2, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms,

is a cyclohexyl group or a phenyl group, at least two of

are a phenyl group, and at least one of the at least two phenyl groups has one or more hydrogen group replaced with a fluorine group, each of Z1, Z2, and Z3 is independently a hydrogen group or a fluorine group.

In an exemplary embodiment, the liquid crystal composition may further contain a compound represented by the following Chemical Formula 3 in an amount of about 0.001 weight percent to about 5 weight percent based on an entire weight of the liquid crystal composition.

Wherein, in Chemical Formula 3, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms,

is a cyclohexyl group or a phenyl group, at least one

is a phenyl group, and one or more hydrogen group of the at least one phenyl group is replaced with a fluorine group, and each of Z1, Z2, Z3, and Z4 is independently a hydrogen group or a fluorine group.

According to an exemplary embodiment, there is provided a liquid crystal composition having a dielectric anisotropy of about −1.5 to about −2.5 and a refractive index anisotropy of about 0.090 to about 0.120.

In an exemplary embodiment, the liquid crystal composition may include: about 10 weight percent to about 30 weight percent of a compound represented by following Chemical Formula 1, based on the total weight of the liquid crystal composition.

Where, in Chemical Formula 1, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms.

In an exemplary embodiment, the liquid crystal composition may further include: a compound represented by the following chemical formula 2 in an amount of about 0.01 weight percent to about 10 weight percent based on the entire weight of the liquid crystal composition.

Where, in Chemical Formula 2, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms,

is a cyclohexyl group or a phenyl group at least two of

are a phenyl group, and at least one of the at least two phenyl groups has one or more hydrogen group replaced with fluorine group, and each of Z1, Z2, and Z3 is independently a hydrogen group or a fluorine group.

In an exemplary embodiment, the compound represented by the Chemical Formula 2 may be a compound represented by the following Chemical Formula 8.

Where, in chemical formula 8, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms.

In an exemplary embodiment, the liquid crystal composition may further include: a compound represented by following Chemical Formula 3 in an amount of about 0.001 weight percent to about 5 weight percent based on the entire weight of the liquid crystal composition.

Where, in Chemical Formula 3, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms,

is a cyclohexyl group or a phenyl group, at least one

is a phenyl group, and one or more hydrogen group of the at least one phenyl group is replaced with a fluorine group, and each of Z1, Z2, Z3, and Z4 is independently a hydrogen group or a fluorine group.

In an exemplary embodiment, the compound represented by Chemical Formula 3 may be a compound represented by following Chemical Formula 12.

Where, in Chemical Formula 12, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms or a fluoroalkoxy group having one to ten carbon atoms.

In an exemplary embodiment, the liquid crystal composition may include: a low margin temperature in a range of about −40° C. to about −20° C., and a high margin temperature in a range of about 90° C. to about 100° C.

Embodiments of the invention provided at least one of the following advantages.

According to an exemplary embodiment, there is provided a liquid crystal composition having wide temperature range to maintain the nematic phase and low viscosity by having a relatively small dielectric anisotropy.

According to an exemplary embodiment, there is provided a liquid crystal display having a wide operating temperature range without high power consumption, which can be applied to various fields of display device.

Also, since the transmittance and contrast of the liquid crystal display device are good, and the response speed is improved, the display quality is also improved.

However, the effects of the invention are not restricted to those set forth herein. The above and other effects of the invention will become more apparent to one of skill in the art to which the invention pertains by referencing the claims.

DETAILED DESCRIPTION

Features of the invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of preferred embodiments and the accompanying drawings.

The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the invention will only be defined by the appended claims.

Hereinafter, embodiments of the invention will be described with reference to the attached drawings.

FIG. 1is a schematic block diagram of an embodiment of a liquid crystal display device.

Referring toFIG. 1, an embodiment of a liquid crystal display device a display area DA and a non-display area (not illustrated). The display area DA is an area in which an image is visible, and the non-display area (not illustrated) is an area in which no image is visible. The outline of the display area DA is surrounded by the non-display area (not illustrated).

The display area DA includes a plurality of first gate lines GL1extending in one direction (e.g., a row direction), a plurality of second gate lines GL2extending in the one direction, a plurality of data lines DL extending in the other direction (e.g., a column direction) intersecting with the one direction, and a plurality of pixel areas PX formed in an area in which the first and second gate lines GL1, GL2and the data line DL intersect with one another. The plurality of pixel areas PX may be arranged in the row direction and in the column direction and may be disposed in a substantially matrix shape.

Each pixel area PX may uniquely display one color of the primary colors to achieve the color display. Examples of the primary colors may include red, green and blue.

The non-display area (not illustrated) may be a light blocking area. In the non-display area of the liquid crystal display device, a gate driver (not illustrated) that provides a gate signal to the pixel areas PX of the display area DA, and a data driver that provides a data signal (not illustrated), may be disposed. The first gate lines GL1, the second gate lines GL2, and the data lines DL extend from the display area DA to the non-display area, and may be electrically connected to the respective drive units.

The gate driver may generate a first gate signal and a second gate signal capable of activating each pixel area PX of the display area DA depending on the gate driver control signal, and may transmit the first and second gate signals to the corresponding first gate line GL1and the second gate line GL2.

Further, the data driver may generate a data signal, including a data voltage depending on a video data signal and the data driver control signal, and may transmit the data signal to the corresponding data line DL. The data voltage may change in polarity for each frame.

Hereinafter, an embodiment of the pixels constituting the liquid crystal display device will be described in detail.

FIG. 2is a plan view of some of the pixels of the liquid crystal display device ofFIG. 1.FIG. 3is a cross-sectional view taken along line ofFIG. 2.

FIG. 2illustrates four pixel areas among the plurality of pixel areas arranged in a matrix shape. The four pixel areas include a first pixel area11aand a second pixel area11b.Other pixel areas which are not illustrated inFIG. 2include the same column as the first pixel area11aand have substantially the same configuration and arrangement as the first pixel area11a,while other pixel areas include the same column as the second pixel area11band may have substantially the same configuration and arrangement as the second pixel area11b.Further, the pixel areas constituting a single row may be repeatedly disposed, while the first pixel area11aand the second pixel area11bform a basic unit.

Referring toFIGS. 2 and 3, the first substrate101may include a first base substrate110, one or more thin film transistors131,132,133,134, a color filter150, one or more sub-pixel electrodes171,172,173,174, a first alignment film190, a plurality of protective films/insulation films, and the like.

The first base substrate110is a transparent insulating substrate which may be formed of substances having excellent permeability, heat resistance and chemical resistance. For example, the first base substrate110may be a silicon substrate, a glass substrate, or a plastic substrate.

A gate wiring layer is disposed on the first base substrate110. The gate wiring layer includes a plurality of first gate lines GL1i,GLli+1, a plurality of second gate lines GL2i,GL2i+1, and a plurality of gate electrodes131a,132a,133a,134a.

The first gate line GL1i extends approximately along a first direction D1. The first gate electrode131aprotrudes downward from the first gate line GL1iand may be integrally formed without a physical boundary to each other. Also, the second gate electrode132aprotrudes downward from the first gate line GL1iand is integrally formed, but may be located on the right side of the first gate electrode131a.A first gate signal provided from the first gate line GL1imay be applied to the first and second gate electrodes131a,132a.Similarly, the second gate line GL2iextends approximately along the first direction D1substantially in parallel to the first gate line GL1i.The third gate electrode133aprotrudes upward from the second gate line GL2iand may be integrally formed without a physical boundary to each other. Further, the fourth gate electrode134aprotrudes upward from the second gate line GL2iand is integrally formed, but may be located on the right side of the third gate electrode133a.A second gate signal provided from the second gate line GL2imay be applied to the third and fourth gate electrodes133a,134a.

The gate wiring layer may be formed by patterning a first metal layer containing an element selected from one or more of tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu), silver (Ag), chromium (Cr) or neodymium (Nd), or an alloy material, or a compound mainly containing the element, after formation of the first metal layer. The patterning may be performed, using a mask process, and using other methods known to be capable of forming a pattern.

A gate insulating film121is disposed on the gate wiring layer and over the entire surface of the first base substrate110. The gate insulating film121is made of an electrically insulating material, and may electrically insulate the layer located thereon and the layer located below it from each other. Examples of the material forming the gate insulating film121may include one or more of silicon nitride (SiNx), silicon oxide (SiOx), silicon nitride oxide (SiNxOy), and silicon oxynitride (SiOxNy). The gate insulating film may be formed of a multi-film structure which includes at least two insulating layers having different physical properties.

A semiconductor material layer is disposed on the gate insulating film121. The semiconductor material layer includes a plurality of semiconductor layers131b,132b,133b,134b.The first semiconductor layer131bmay be at least partially disposed in an area in which it is superimposed with the first gate electrode131a.The first semiconductor layer131bperforms the role of a channel in the thin film transistor, and may turn on or turn off the channel depending on the voltage provided to the gate electrode. Similarly, the second semiconductor layer132bis at least partially disposed in an area in which it is superimposed with the second gate electrode132a,the third semiconductor layer133bis at least partially disposed in an area in which it is superimposed with the third gate electrode133a,and the fourth semiconductor layer134bmay be at least partially disposed in an area in which it is superimposed with the fourth gate electrode134a.

The semiconductor material layer may be formed by patterning a semiconductor material layer including a semiconductor material, such as amorphous silicon, polycrystalline silicon, or an oxide semiconductor.

A data wiring layer is disposed on the semiconductor material layer. The data wiring layer includes a plurality of data lines DLj, DLj+1, DLj+2, a plurality of source electrodes131c,132c,133c,134cand a plurality of drain electrodes131d,132d,133d,134d.

The first data line DLj extends approximately along the second direction D2to intersect with the first and second gate lines GL1i,GL2i.In addition, the second data line DLj+1and the third data line DLj+2also extend approximately along the second direction D2substantially in parallel to the first data line DLj to intersect with the first and second gate lines GL1i,GL2i.The first to third data signals may be applied to each of the first to third data lines DLj, DLj+1, DLj+2.

A plurality of pixel areas11a,11bis defined in an area surrounded by the plurality of first and second gate lines GL1i,GL2iand the plurality of data lines DLj, DLj+1, DLj+2. The plurality of each of the pixel areas11a,11bmay be areas which are independently operated by a plurality of thin film transistors131,132,133,134connected by the adjacent first and second gate lines and the data lines.

The first source electrode131cand the first drain electrode131dare disposed on the first gate electrode131aand the first semiconductor layer131bso as to be spaced apart from each other. The first source electrode131cmay have a shape that at least partially surrounds the first drain electrode131d.For example, the first source electrode may have a C-shape, a U-shape, an inverted C-shaped, or an inverted U-shape. The first source electrode131cprotrudes to the right side from the first data line DLj and may be integrally formed with the first data line DLj without a physical boundary. The first drain electrode131dmay be electrically connected to the first sub-pixel electrode171in the first pixel area11a.

Further, the second source electrode132cand the second drain electrode132dare disposed on the second gate electrode132aand the second semiconductor layer132bso as to be spaced apart from each other. The second source electrode132cprotrudes to the left from the second data line DLj+1and may be integrally formed with the second data line DLj+1. The second drain electrode132dmay be electrically connected to the second sub-pixel electrode172in the first pixel area11a.

Further, the third source electrode133cand the third drain electrode133dare disposed on the third gate electrode133aand the third semiconductor layer133bso as to be spaced apart from each other. The third source electrode133cprotrudes to the right side from the second data line DLj+1and may be integrally formed with the second data line DLj+1. The third drain electrode133dmay be electrically connected to the third sub-pixel electrode173in the second pixel area11b.

Furthermore, the fourth source electrode134cand the fourth drain electrode134dare disposed on the fourth gate electrode134aand the fourth semiconductor layer134bso as to be spaced apart from each other. The fourth source electrode134cprotrudes to the left side from the third data line DLj+2and may be integrally formed with the third data line DLj+2. The fourth drain electrode134dmay be electrically connected to the fourth sub-pixel electrode174in the second pixel area11b.

The data wiring layer may be formed by patterning a second metal layer. The second metal layer may include a refractory metal, such as silver (Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), tungsten (W), aluminum (Al), tantalum (Ta), molybdenum (Mo), cadmium (Cd), zinc (Zn), iron (Fe), titanium (Ti), silicon (Si), germanium (Ge), zirconium (Zr), or barium (Ba), or alloys thereof, or the second metal layer containing the metal nitride, after formation of the second metal layer.

An ohmic contact layer (not illustrated) may be disposed between the semiconductor material layer and the data wiring layer. The ohmic contact layer may contain an n+ hydrogenated amorphous silicon material doped with n-type impurity at a high concentration or may contain silicide.

Each of the first to fourth gate electrodes131a,132a,133a,134, the first to fourth semiconductor layers131b,132b,133b,134b,the first to fourth source electrodes131c,132c,133c,134c,and the first to fourth drain electrodes131d,132d,133d,134dconstitutes a thin film transistor which is a three terminal element.

A protective film122is disposed on the data wiring layer and over the entire surface of the first base substrate110. The protective film122may be formed of an organic film and/or an inorganic film and may have a single film or multi-film structure. The protective film122may prevent wirings formed below, or the semiconductor layer of the thin film transistor, from being exposed and coming into direct contact with the organic material.

A color filter150may be disposed on the protective film122in the area superimposed with the pixel area. The color filter150may allow light of a specific wavelength band to selectively pass therethrough. The color filter150may be disposed between the two adjacent data lines, and color filters that allow light of different wavelength bands to pass may be disposed in different pixel areas adjacent to each other. For example, a red color filter may be disposed in the first pixel area, and a green color filter may be disposed in the second pixel area adjacent to the first pixel area.

AlthoughFIG. 3illustrates a color filter-on array in which the color filter150is disposed on the first substrate101, in some embodiments, an array-on color filter structure in which the color filter is formed below the thin film transistor may be adopted, or alternatively, the color filter may be disposed on the second substrate.

An insulating layer160is disposed on the color filter150over the entire surface of the protective film122. The insulating layer160may contain an organic material. The insulating layer160may make the heights of the plurality of components laminated on the first base substrate110uniform.

Contact holes141,142,143, and144are formed in the protective film122and the insulating layer160so that the first to fourth drain electrodes131d,132d,133d,134dare partially exposed. The first to fourth drain electrodes131d,132d,133d,134dmay be electrically connected to each of the first to fourth sub-pixel electrodes171,172,174through the first to fourth contact holes141,142,143,144.

The first sub-pixel electrode171and the second sub-pixel electrode172may be disposed on the top of the insulating layer160in the first pixel area11aand on the top of the first and second drain electrodes131d,132dexposed by the first and second contact holes141,142. Similarly, the third sub-pixel electrode173and the fourth sub-pixel electrode174may be disposed on the top of the insulating layer160in the second pixel area11band on the top of the third and fourth drain electrodes133d,134dexposed by the third and fourth contact holes143,144. AlthoughFIG. 3illustrates a case where the first sub-pixel electrode171and the second sub-pixel electrode172are disposed on the same layer, as an alternative to the illustrated configuration, a predetermined insulation layer may be disposed on the first sub-pixel electrode, and the second sub-pixel electrode may be disposed on the insulating layer.

The first to fourth sub-pixel electrodes171,172,173,174may be transparent electrodes formed by patterning the third metal layer. Examples of a material which forms the third metal layer may include, but not limited to, indium tin oxide (ITO), indium zinc oxide (IZO) or the like.

The first sub-pixel electrode171in one pixel area, e.g., the first pixel area11a,may form a fringe field together with the second sub-pixel electrode172disposed in the same pixel area and a common electrode250(to be described later), thereby controlling the liquid crystal molecules in the liquid crystal layer300.

The first sub-pixel electrode171includes a plurality of first branch electrode sections171a,a first connection electrode section171bwhich connects at least one end of the plurality of first branch electrode sections171a,and a first protrusion electrode section171c,which protrudes from the first connection electrode section171bin the direction of the first contact hole141.

The first branch electrode section171amay have a bar shape that is symmetrically bent on the basis of the substantially central portion of the first pixel area11a.The directions of the major fringe field may be differently formed on the upper side and the lower side on the basis of the central portion of the first pixel area11aby the first sub-pixel electrode171having the bar-shaped structure, and accordingly, two domains may be formed in a single pixel area. The movement of the liquid crystal molecules in different domains differs within a single pixel area, and as a result, the arrangement of the long axis of the liquid crystal molecules becomes different, and thus, the color shift phenomenon observed at a particular orientation angle may be reduced.

The first protrusion electrode section171cis electrically connected to the first drain electrode131dthrough the first contact hole141to receive the provision of the data voltage transmitted from the first data line DLj. The first connection electrode section171bserves to connect the first protrusion electrode section171cwith the plurality of first branch electrode sections171a.

Further, the second sub-pixel electrode172includes a plurality of second branch electrode sections172a,a second connection electrode section172bconnecting at least one of the plurality of second branch electrode sections172ato each other, and a second protrusion electrode section172cwhich protrudes from at least one of the plurality of second branch electrode sections172ain the direction of the second contact hole142.

The second branch electrode section172ais disposed between the two adjacent first electrode sections171a,and may have a shape corresponding to the first branch electrode section171a.That is, on a section perpendicular to the extension direction of the first and second branch electrode sections171a,172a,the first branch electrode section171aand the second branch electrode section172amay be arranged in a mutually alternating manner. Further, the first electrode section171aand the second branch electrode section172amay receive the provision of the data voltages having different polarities from each other.

The first sub-pixel electrode171and the second sub-pixel electrode172having such an arrangement form an electric field together with the common electrode250, and may mutually form an electric field. Thus, control of the liquid crystals is improved, and there is an added effect of being able to reduce the driving voltage of the liquid crystal display device.

Meanwhile, the second protrusion electrode section172cis electrically connected to the second drain electrode132dthrough the second contact hole142to receive the provision of the data voltage transmitted from the second data line DLj+1. The second connection electrode section172bserves to connect the second protrusion electrode section172cwith the plurality of second branch electrode sections172a.

Similarly, the third sub-pixel electrode173in the second pixel area11bmay form a fringe field together with the fourth sub-pixel electrode174and the common electrode250disposed in the same pixel area. Each of the third sub-pixel electrode173and the fourth sub-pixel electrode174may have substantially the same shape and arrangement as those of the first sub-pixel electrode171and the second sub-pixel electrode172.

Thus, the third sub-pixel electrode173is connected to the second data line DLj+1to receive the provision of the same data voltage as the second sub-pixel electrode172, and the fourth sub-pixel electrode174may receive the provision of the data voltage transmitted from the third data line DLj+2.

FIG. 4is a comparative diagram comparing the cross-section taken along line IVa-IVa′ with the cross-section taken along the IVb-IVb′ ofFIG. 2, which shows the cross-sectional view illustrating the polarity of the voltage applied to the first to fourth sub-pixel electrodes171,172,173,174in a single frame interval.

As described above, the first sub-pixel electrode171in the first pixel area11ais electrically connected to the first gate line GL1i and the first data line DLj, the second sub-pixel electrode172in the first pixel area11ais electrically connected to the first gate line GL1iand the second data line DLj+1, the third sub-pixel electrode173in the second pixel area11bis electrically connected to the second gate line GL2iand the second data line DLj+1, and the fourth sub-pixel electrode174in the second pixel area11bis electrically connected to the second gate line GL2iand the third data line DLj+2.

As illustrated inFIG. 4, the data voltage applied to the data lines forming the odd-numbered rows in a single frame interval, for example, the first data voltage and the third data voltage applied to the first data line DLj and the third data line DLj+2, have the same polarity with respect to the common voltage (i.e. the reference voltage) applied to the common electrode250, and the data voltage applied to the data lines adjacent to each other, for example, the first data voltage and second data voltage applied to the first data line DLj and the second data line DLj+1, respectively, may have different polarities from each other with respect to the common voltage.

In operation of the pixel in an arbitrary frame interval, when the first gate signal is applied to the first gate line GL1iin a frame, the first thin film transistor131connected thereto is turned on. Thus, the first data voltage having the positive polarity provided from the first data line DLj charges the first sub-pixel electrode171through the first thin film transistor131which is turned on.

At the same time, the second thin film transistor132connected to the first gate line GL1iis also turned on, and thus, the second data voltage having the negative polarity provided from the second data line DLj+1charges the second sub-pixel electrode172through the second TFT132which is turned on.

Thus, the data voltages having the different polarities from each other may be charged to the first sub-pixel electrode171and the second sub-pixel electrode172of the first pixel area11ain a single frame interval without an additional data line, and a strong electric field may be formed between the first sub-pixel electrode171and the second sub-pixel electrode172.

In addition, when the second gate signal is applied to the second gate line GL2i,the third thin film transistor133connected thereto is turned on. Thus, the second data voltage having the negative polarity provided from the second data line DLj+1charges the third sub-pixel electrode173through the third thin film transistor133which is turned on.

At the same time, the fourth thin film transistor134connected to the second gate line GL2iis also turned on, and thus, the third data voltage having the positive polarity provided from the third data line DLj+2charges the fourth sub-pixel electrode174through the fourth thin film transistor134which is turned on.

Thus, data voltages having different polarities from each other may be charged to the third sub-pixel electrode173and the fourth sub-pixel electrode174of the second pixel area11bin a single frame interval without an additional data line, and as a result, a strong electric field may be formed between the third sub-pixel electrode173and the fourth sub-pixel electrode174.

In the next frame, the first and third data voltages having the negative polarity are provided to the first and third data lines, and the second data voltage having the positive polarity is provided to the second data line, and this process may be repeated.

That is, the voltages having different polarities may be applied to the plurality of sub-pixel electrodes in a pixel area without adding a separate data line At the same time, by reversing the polarity of the data voltage applied to each data line for each frame interval, it is possible to minimize a flicker phenomenon which can be visually recognized by the viewer.

Meanwhile, a predetermined voltage having a value between the first data voltage and the second data voltage may be applied to the common electrode250during a single frame interval.

FIG. 5is a cross-sectional view illustrating the behavior of the liquid crystal molecules in the first pixel area11aofFIG. 2.

Referring toFIG. 5, the mutually different voltages are applied to the first sub-pixel electrode171, the second sub-pixel electrode172, and the common electrode250of the first pixel area11ain the single frame interval. Thus, a first electric field E1may be formed between the common electrode250and the first sub-pixel electrode171, a second electric field E2may be formed between the common electrode250and the second sub-pixel electrode172, and a third electric field E3may be formed between the first sub-pixel electrode171and the second sub-pixel electrode172. In an exemplary embodiment, the absolute value of the first electric field E1and the absolute value of the second electric field E2may be the same.

In an initial state in which an electric field is not applied to the liquid crystal layer, the long axes of the liquid crystal molecules LC are oriented parallel to a direction approximately perpendicular to the extension direction of the pixel electrode branch section, i.e., the first direction D1. When the first to third electric fields E1, E2, E3are formed, the long axes of the liquid crystal molecules may be aligned in a direction perpendicular to the electric field.

Specifically, when the first electric field E1is formed between the common electrode250and the first sub-pixel electrode171, the liquid crystal molecules LC having the long axes oriented in the first direction D1near the first electric field E1, are rotated on a plane so that the long axes may be aligned in a direction perpendicular to the first electric field E1. When the second electric field E2is formed between the common electrode250and the second sub-pixel electrode172, the liquid crystal molecules LC having the long axes oriented in the first direction D1near the second electric field E2, rotate on a plane so that the long axes may be aligned in a direction perpendicular to the second electric field E2. When the third electric field E3is formed between the first sub-pixel electrode171and the second sub-pixel electrode172, the liquid crystal molecules LC having the long axes oriented in the first direction D1near the third electric field E3, rotate on a plane so that the long axes may be aligned in a direction perpendicular to the third electric field E3. Furthermore, liquid crystal molecules adjacent to the liquid crystal molecules rotated by the first to third electric fields E1, E2, and E3, have the same directivity via the collision process between the liquid crystal molecules, and thus the final alignment direction of the liquid crystal molecules in the first pixel area11amay be determined. Thus, the polarization components of the light incident from a light source (not illustrated) positioned below the liquid crystal display panel change and light passes therethrough. That is, by forming a plurality of electric fields in a single pixel area, it is possible to minimize variation in the alignment of liquid crystal molecules beyond the control force of the electric field, thereby improving control of the alignment of the liquid crystal molecules.

Referring toFIGS. 2 and 3again, a first alignment film190may be formed on the entire surface of the first and second sub-pixel electrodes171,172of the first pixel area11aand over the entire surface the third and fourth sub-pixel electrodes173,174of the second pixel area11b.The first alignment film190has an anisotropy and may arrange the liquid crystal molecules of the liquid crystal layer300which are adjacent to the first alignment film190, to be aligned in a particular direction relative to the plane of the alignment film. The first alignment film190may be a horizontal alignment film.

Subsequently, a second substrate201will be described. The second substrate201may include a second base substrate210, a light blocking member220, an overcoat layer230, a common electrode250and a second alignment film290.

The second base substrate210may be a transparent insulating substrate like the first base substrate110. The light blocking member220is disposed on the second base substrate210. The light blocking member220may be, for example, a black matrix. The light blocking member220may be disposed in a boundary area between the plurality of pixel areas, that is, an area superimposed with the data lines, and an area superimposed with the thin film transistor and the plurality of gate lines. That is, a plurality of pixel areas is partitioned by the light blocking member220and may prevent a light leakage defect that may occur in a boundary area between the pixel areas.

The overcoat layer230is disposed on the light blocking member220across the entire surface of the second base substrate210. The overcoat layer230prevents the light blocking member220from lifting off of the second base substrate210, and makes the height of the components laminated on the second base substrate210uniform.

The common electrode250may be placed on the overcoat layer230. The common electrode250may be a transparent electrode formed by patterning the fourth metal layer. The common electrode250may be disposed to overlap most areas except for some areas of each of the pixel areas11a,11b.As described above, the common electrode250may control the liquid crystal molecules by forming a fringe field together with the first to fourth sub-pixel electrodes171,172,173,174. The material forming the fourth metal layer may be the same as or different from the material forming the third metal layer. The second alignment film290may be disposed on the common electrode250over the entire surface.

The first substrate101and the second substrate201are disposed to maintain a predetermined cell gap and to face each other. In an exemplary embodiment, the cell gap of the liquid crystal display device may be, but is not limited to, about 2.8 μm to about 3.4 μm.

The liquid crystal layer300is interposed between the first substrate101and the second substrate201. The liquid crystal layer300contains a liquid crystal composition having a negative dielectric anisotropy of about −2.5 to about −1.5. Moreover, the rotational viscosity of the liquid crystal composition may be about 80 millipascals (mPa) to about 110 mPa.

Further, the refractive index anisotropy of the liquid crystal composition may be about 0.090 to about 0.120 or less. By controlling the product (Δnd) of the refractive index anisotropy of the liquid crystal composition, the cell gap of the liquid crystal display device, and the rotational viscosity of the liquid crystal composition, it is possible to improve the response speed of the liquid crystal display device.

In addition, the low margin temperature of the liquid crystal composition may be about −50° C. to about −30° C., and the high margin temperature may be about 90° C. to about 110° C. Since the margin temperature range capable of maintaining the nematic phase of the liquid crystal composition is about −50 to about 110° C., the liquid crystal display device including the liquid crystal composition may ensure a wide operating temperature range.

In addition, the liquid crystal composition may contain a compound represented by the following chemical formula 1 in an amount of about 10 weight percent (wt %) to about 30 weight percent. The liquid crystal composition may further contain a compound represented by the following Chemical Formula 2 in an amount of about 0.01 wt % to about 10 wt %, and may further contain a compound represented by the following Chemical Formula 3 in an amount of about 0.001 wt % to about 5 wt %. The weight percents are based on the entire liquid crystal composition.

In Chemical Formulas 1 to 3, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms, or a fluoroalkoxy group having one to ten carbon atoms. In Chemical Formulas 2 and 3,

is a cyclohexyl group or a phenyl group. In Chemical Formula 2, each of Z1, Z2, and Z3 is independently a hydrogen group or a fluorine group, at least two of

is a phenyl group, and at least one of the at least two phenyl groups has one or more hydrogen group replaced with fluorine groups. In Chemical Formula 3, each of Z1, Z2, Z3, and Z4 is independently a hydrogen group or a fluorine group, at least one of

is a phenyl group, and one or more hydrogen group of the at least one phenyl group is replaced with a fluorine group.

Since the fluorine substituents of the liquid crystal molecules contained in the liquid crystal composition induce the negative dielectric anisotropy of the liquid crystal composition, and have a high electronegativity, the fluorine substituents increase the attractive force between the liquid crystal molecules and induce the smetic phase which easily induces crystallization of the liquid crystal molecules. That is, when the absolute value of the dielectric anisotropy is large, the viscosity of the liquid crystal compositions increases, the response speed of the liquid crystal display device is reduced, and a low-temperature margin may be disadvantageous.

In an embodiment, the liquid crystal composition has an effect of being able to maintain the sufficient response speed, since the ranges of low-temperature margin and high-temperature margin capable of maintaining smetic phase are wide and the viscosity is low. This is achieved lowering the relative content of the fluorine substituent in the composition.

Hereinafter, an embodiment of the liquid crystal composition will be described in detail referring to a production example and a comparative example.

PRODUCTION EXAMPLE AND COMPARATIVE EXAMPLE

The liquid crystal compositions including the listed components and their amounts in the composition (% by weight) were prepared as illustrated in Table 1 below.

Chemical formulas 4 to 12 in Table 1 may be expressed as follows.

In chemical formulas 4 to 12, each of X and Y is independently an alkyl group having one to ten carbon atoms, an alkenyl group having two to ten carbon atoms, an alkoxyl group having one to ten carbon atoms, a fluoroalkyl group having one to ten carbon atoms, a fluoroalkenyl group having two to ten carbon atoms, or a fluoroalkoxy group having one to ten carbon atoms.

Next, the following experiments were performed using the liquid crystal compositions of production examples 1 to 4 and comparative examples 1 and 2.

EXPERIMENTAL EXAMPLE 1

Measurement of Major Physical Properties of Liquid Crystal Composition

The major physical properties of the liquid crystal compositions prepared by production examples 1 to 4 and comparative examples 1 and 2 were determined.

In Table 2, Δε means the dielectric anisotropy of the liquid crystal composition, An means the refractive index anisotropy of the liquid crystal composition, and γ1means the rotational viscosity having the unit of millipascal second (mPa·s). Further, the high-temperature margin refers to the upper limit temperature of the liquid crystal composition to maintain the nematic phase, and the low-temperature margin refers to the minimum temperature of the liquid crystal composition to maintain the nematic phase.

As shown in Table 2, the liquid crystal composition of production examples 1 to 4 has have a dielectric anisotropy of about −2.5 to about −1.5, and a refractive index anisotropy of about 0.094 to about 0.114. Further, the liquid crystal composition of production examples 1 to 4 has the high margin temperature of about 100° C. and the low-margin temperature of about −40° C., and thus the nematic phase may be maintained across a wide temperature range.

EXPERIMENTAL EXAMPLE 2

Measurement of Major Driving Characteristics of Panel

An embodiment of a liquid crystal display device including the liquid crystal composition prepared by production examples 1 to 4 and comparative examples 1 and 2 was manufactured, and the major driving characteristics of the manufactured liquid crystal displays were measured.

In Table 3, the maximum transmittance is a value (i.e. percentage) obtained by comparing the light transmittance of the liquid crystal display device of the experimental examples with the light transmittance of a reference liquid crystal display device as a comparative target and which is assumed to be 100%.

As shown in Table 3, the liquid crystal display device including the liquid crystal compositions of production examples 1 to 4 has the maximum relative transmittance of about 120% or more and exhibits sufficient transmittance. Also, it is possible to understand that the response speed is about 20 to 25 milliseconds (ms) and that the liquid crystal display device has a relatively excellent response speed. Further, the driving voltage is about 5.5 V to about 6.5 V and thus the low-voltage driving is possible.

Meanwhile, the results show that the liquid crystal display device including the liquid crystal composition of comparative example 1 has a relatively high driving voltage of about 7.5 V, which is not suitable for use in the liquid crystal display device.

Further, the liquid crystal display device including the liquid crystal composition of comparative example 2 has a high response speed of about 33 ms or more, which is not suitable for use in the liquid crystal display device.