Liquid crystal display device and method of manufacturing the same

A liquid crystal display device includes an array substrate, an opposite substrate and a liquid crystal display layer. The array substrate includes a pixel electrode and a lower reactive mesogen layer. The pixel electrode includes a plurality of slit portions disposed on a plurality of domains in different directions. The lower reactive mesogen layer is disposed on the pixel electrode to induce an inclined direction of liquid crystal molecules. The opposite substrate includes an upper substrate. An upper reactive mesogen layer is disposed on a common electrode of the opposite substrate. The liquid crystal layer includes liquid crystal molecules arranged to have a pretilt angle between a surface of the lower reactive mesogen layer and a surface of the upper reactive mesogen layer.

This application claims priority to Korean Patent Application No. 2008-106521 filed on Oct. 29, 2008, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a liquid crystal display (“LCD”) device and a method of manufacturing the LCD device. More particularly, exemplary embodiments of the present invention relate to an LCD device capable of enhancing display quality such as a viewing angle and a response speed, and a method of manufacturing the LCD device.

2. Description of the Related Art

In a liquid crystal display (“LCD”) device, a voltage is applied to an electric field generating electrode to provide the liquid crystal layer with an electric field, and an arrangement of liquid crystal molecules of the liquid crystal layer is controlled in response to the electric filed, thereby displaying images.

In order to obtain a high contrast ratio and a wide viewing angle, a patterned vertical alignment (“PVA”) mode LCD device has been developed. In the PVA mode LCD device, an opening portion (hereinafter, a slit portion) of a slit shape is formed through the electric field generating electrode, and liquid crystals are vertically aligned to realize multiple domains.

For a medium or small sized mobile LCD device, in order to decrease the slit portion which decreases an aperture ratio, a micro slit mode LCD device or a super patterned vertical alignment (“SPVA”) mode LCD device has been developed. In the micro slit mode LCD device, a micro slit portion is only formed through a lower electrode of the electric field generating electrodes to provide a direction property to the liquid crystal, and an upper electrode is formed as a flat continuous plate in which an opening portion is not formed.

In a vertical alignment (“VA”) mode, such as the PVA mode and the micro slit mode, a rubbing is not directly performed on an alignment layer, however, a light alignment method may be employed which aligns liquid crystal by inducing anisotropy to an alignment layer through light irradiating.

Polarized UV lights are irradiated to a light bridge high-molecular copolymer including a mesogenic group of a liquid crystal property, also called a reactive mesogen, to induce anisotropy, and then anisotropy of the alignment layer is enhanced to align liquid crystal by heat processing on the light bridge high-molecular copolymer.

BRIEF SUMMARY OF THE INVENTION

Since a reactive mesogen may be employed to induce anisotropy to an alignment layer through light irradiating, there may be technical difficulties in manufacturing an LCD device when the reactive mesogen is used. For example, the reactive mesogen is not cured at a surface of the alignment layer, and the reactive mesogen remains within an inner area of the liquid crystal layer. The remaining reactive mesogen may be additionally cured by a backlight of the LCD device, however, the cured amounts of the reactive mesogen in accordance with varying areas are different from each other so that a pretilt angle of liquid crystal may be non-uniform between the varying areas. As a result, an afterimage may be undesirably viewed on a display screen.

Exemplary embodiments of the present invention provide an LCD device having improved display quality, such as a viewing angle and a response speed.

Exemplary embodiments of the present invention provide a method of manufacturing the above-mentioned LCD device.

An exemplary embodiment of an LCD device includes an array substrate, an opposite substrate and a liquid crystal layer. The array substrate includes a lower substrate, a pixel electrode and a lower reactive mesogen layer. The lower substrate includes a switching part disposed thereon. The pixel electrode is disposed on a unit pixel area of the lower substrate to contact with the switching part. The pixel electrode includes a plurality of slit portions disposed on a plurality of domains and extended in different directions. The lower reactive mesogen layer is disposed on the pixel electrode to induce a slant direction of liquid crystal molecules. The opposite substrate includes an upper substrate opposite to the lower substrate. A common electrode is disposed on the upper substrate and faces the pixel electrode, and an upper reactive mesogen layer is disposed on the common electrode. The liquid crystal layer includes liquid crystal molecules affected to have a pretilt angle and disposed between a surface of the lower reactive mesogen layer and a surface of the upper reactive mesogen layer.

In an exemplary embodiment of the present invention, the array substrate may further include a lower alignment layer disposed between the pixel electrode and the lower reactive mesogen layer. The opposite substrate may further include an upper alignment layer disposed between the common electrode and the upper reactive mesogen layer. A weight of uncured reactive mesogen material diffused from the lower and upper reactive mesogen layers to the liquid crystal layer, is no more than about 20 weight percent (wt %) with respect to a weight of the lower and upper reactive mesogen layers. The LCD device may further include a diffusion stop layer disposed on surfaces of the lower reactive mesogen layer and the upper reactive mesogen layer to block the reactive mesogen layer from being diffused to the liquid crystal layer.

In an exemplary embodiment of the present invention, the pixel electrode may include a first pixel electrode and a second pixel electrode which are disposed on the unit pixel area and respectively receive different pixel voltages. The slit portions may be disposed on a plurality of domains defined on the first and second pixels, respectively, in the different directions. The common electrode corresponding to the first and second pixel electrodes may have a substantially flat plate shape in which an opening is not disposed. The lower alignment layer and the upper alignment layer may be aligned to be vertically arranged to a long axis of the liquid crystal molecules when an electric field applied to the liquid crystal layer is turned off. Alternatively, the lower alignment layer and the upper alignment layer may be aligned to arrange a long axis of the liquid crystal molecules in an extending direction of the slit portion at each of the domains when an electric field applied to the liquid crystal layer is turned off.

An exemplary embodiment provides a method of manufacturing an LCD device. In the method, a lower alignment layer is disposed on an array substrate including a pixel electrode including a plurality of slit portions inducing an alignment direction of liquid crystal molecules. A lower reactive mesogen layer is disposed on the lower alignment layer. A liquid crystal layer is disposed on the lower reactive mesogen layer. An opposite substrate is coupled with the array substrate. Light is irradiated at a condition in which an electric field is applied to the liquid crystal layer through the pixel electrode to provide a pretilt angle to the liquid crystal molecules at a surface of the lower reactive mesogen layer.

In an exemplary embodiment of the present invention, in the method, an upper alignment layer may be disposed on a common electrode of the opposite substrate before the coupling with the array substrate, and an upper reactive mesogen layer may be disposed on the upper alignment layer. The common electrode corresponding to the pixel electrode may have a substantially flat plate shape in which an opening is not disposed.

In an exemplary embodiment of the present invention, the lower reactive mesogen layer and the upper reactive mesogen layer may be formed by coating a reactive mesogen blend, including a reactive mesogen, on the lower alignment layer and the upper alignment layer, respectively, through a spray method or a coating method. A weight of uncured reactive mesogen material, which is diffused from the lower and upper reactive mesogen layers to the liquid crystal layer, may be no more than about 20 weight percent (wt %) with respect to an initial weight of the lower and upper reactive mesogen layer. Alternatively, a weight of uncured reactive mesogen material, which is diffused from the lower and upper reactive mesogen layers to the liquid crystal layer, may be no more than about 1.0 weight percent (wt %) with respect to an initial weight of the lower and upper reactive mesogen layer. A diffusion stop layer may be further formed, which reduced or effectively prevents the reactive mesogen layer from being diffused to the liquid crystal layer, on surfaces of the lower reactive mesogen layer and the upper reactive mesogen layer. The diffusion stop layer may be formed through a heat processing or a light reactive processing of surfaces of the lower reactive mesogen layer and the upper reactive mesogen layer before the liquid crystal layer is disposed.

In an exemplary embodiment of the present invention, the lower alignment layer and upper alignment layer may be formed by coating a blend including at least one of photo-reactive polymer of a cinematic series and a polymer of a polyimide series on the pixel electrode and the common electrode. The pixel electrodes may be disposed on a unit pixel area of the array substrate, and the slit portions may be disposed in the different directions on a plurality of domains defined on each of the pixel electrodes. The lower alignment and the upper alignment layer may be aligned so that a long axis of the liquid crystal molecules is vertically aligned. Alternatively, the lower alignment layer and the upper alignment layer may be aligned so that the long axis of the liquid crystal molecules is arranged in an extending direction of the slit portion at each of the domains.

In exemplary embodiments of the LCD device and the method of manufacturing the LCD device, an aperture ratio and a response speed are enhanced, and a generation of an undesired afterimage is decreased, so that display quality may be advantageously enhanced.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a plan view illustrating an exemplary embodiment of an array substrate101employed in a liquid crystal display (“LCD”) device.FIG. 2is an equivalent circuit diagram illustrating an exemplary embodiment of one pixel PX01in the LCD including the array substrate101illustrated inFIG. 1.

Referring toFIGS. 1 and 2, an LCD device includes the array substrate101, an opposite substrate201and a liquid crystal layer180interposed between the array substrate101and the opposite substrate201. Various technologies for enhancing display quality may be employed to the LCD device.

In one exemplary embodiment, a plurality of a pixel electrode, indicated by162and164inFIGS. 1 and 2, is disposed on a single unit pixel area PA01of the LCD device, and receives pixel voltages that are different from each other. A plurality of a micro slit portion, indicated by161and165inFIG. 2, is disposed to extend completely through the pixel electrodes162and164, respectively, in order to enhance a viewing angle by varying alignment directions of liquid crystal molecules. A reactive mesogen layer is disposed on the pixel electrodes162and164, and a common electrode of the opposite substrate201, respectively, in order to enhance a response speed of the liquid crystal. The liquid crystal is aligned to have a pretilt angle directly by the reactive mesogen layer. The LCD device for enhancing display quality, and a method of manufacturing the LCD will be described.

In the illustrated embodiment, the array substrate101includes, as shown inFIGS. 1 and 2, a plurality of a gate line111, a plurality of a data line115, a plurality of a storage line116, the plurality of pixel electrodes162and164, and a switching part. In the illustrated embodiment, two pixel electrodes162and164are disposed on the unit pixel area PA01. A first pixel electrode to which a relatively high level pixel voltage is applied may be denoted as a main pixel electrode, and a second pixel electrode to which a relatively low level pixel voltage is applied may be denoted as a sub-pixel electrode. In the illustrated embodiment ofFIGS. 1 and 2, the main pixel electrode is defined as the first pixel electrode162, and the sub-pixel electrode is defined as the second pixel electrode164.

The first and second pixel electrodes162and164are each electrically connected to a same gate line111, and are each electrically connected to different data lines115. Referring toFIGS. 1 and 2, a pixel of the LCD device is driven in one gate line and two data line (1G2D) method. In the illustrated embodiment, the switching part includes a first switching element122and a second switching element124. The first switching element122electrically connects the first pixel electrode162to a first gate line111and a first data line115. The second switching element124electrically connects the second pixel electrode164to the first gate line111and a second data line115different from the first data line115, such as an adjacent data line115.

The storage line116includes a first (main) portion longitudinally extended in the row direction D1, and substantially parallel with the gate lines111. A plurality of a branch portion is protruded from the first portion and extended in the column direction D2towards the first switching element122and the second switching element124in a plan view. A first branch portion117and a second branch portion118are substantially disposed within the unit pixel area PA01, where a portion of each of the first branch portion117and the second branch portion118overlaps with adjacent data lines115and the first pixel electrode162. A portion of the first (main) portion of the storage line116overlaps boundaries of both the first pixel electrode162and the second pixel electrode164.

The opposite substrate201includes a common electrode disposed to face the first and second pixel electrodes162and164. The first pixel electrode162, the common electrode and the liquid crystal layer180form a first liquid crystal capacitor Clc1, and the second pixel electrode164, the common electrode and the liquid crystal layer180form a second liquid crystal capacitor Clc2. The first pixel electrode162and a first storage line116together form a first storage capacitor Cst1, and the second pixel electrode164and the first storage line116together form a second storage capacitor Cst2.

Pixel voltages of the different levels may be applied to the first and second pixel electrodes162and164, respectively. In one exemplary embodiment, a first pixel voltage applied to the first pixel electrode162is higher than a second pixel voltage applied to the second pixel electrode164. Alternatively, a first pixel voltage applied to the first pixel electrode162is lower than a second pixel voltage applied to the second pixel electrode164. When levels of the first and second pixel voltages are adjusted, images viewed at a side (e.g., not in a front) of a display screen of the LCD device may have substantially close to or the same display characteristics of an image viewed at substantially a front of the display screen of the LCD device. Advantageously, display quality is substantially uniform in accordance with the viewing angle, so that side visibility of the LCD device may be enhanced.

FIG. 3is a flowchart illustrating an exemplary embodiment of a method of manufacturing an LCD device.

Summarizing a method of manufacturing the LCD device of the illustrated embodiment, a lower alignment layer is formed on the array substrate101including a pixel electrode including micro slit portions161and165formed therethrough which determine an alignment direction of liquid crystal (step S10). A lower reactive mesogen layer is formed on the lower alignment layer (step S20). The liquid crystal layer180is disposed on the lower reactive mesogen (“RM”) layer (step S30). The opposite substrate201is combined with the array substrate101(step S40). In a status in which an electric field is applied to the liquid crystal layer180through the first and second pixel electrodes162and164, light is irradiated to the opposite substrate201to provide a pretilt angle to liquid crystal (step S50).

Hereinafter, each manufacturing processes will be detail described.

FIG. 4is a cross-sectional view taken along line I-I′ of an array substrate101ofFIG. 1.FIG. 5is a plan view illustrating an exemplary embodiment of an array substrate101excluding a pixel electrode ofFIG. 1.FIG. 6is a plan view illustrating an exemplary embodiment of a pixel electrode of an array substrate101as illustrated inFIG. 1.

Referring toFIGS. 4,5and6, a lower alignment layer is formed on the array substrate101which includes the first and second pixel electrodes162and164including the micro slit portions161and165, which determine an alignment direction of liquid crystal, formed thereon (step S10).

The array substrate101includes a plurality of a gate line111, a plurality of a data line115, first and second switching elements122and124and first and second pixel electrodes162and164which are disposed on a lower base substrate110. In an exemplary embodiment, the lower base substrate110may include a glass material, but the invention is not limited thereto.

A gate metal is coated on the lower base substrate110The coated gate metal is etched to form the gate lines111. The gate lines111are disposed on the lower base substrate110in parallel with a row direction D1indicated inFIGS. 1 and 5. A portion of each of the gate lines111forms a gate electrode112of a protruding shape. As shown inFIG. 4, a gate insulation layer121is disposed on the gate lines111, and directly contacts both the gate lines111and the lower base substrate110.

A semiconductor layer and a source metal layer are sequentially formed on the gate insulation layer121. The source metal layer and the semiconductor layer are etched to form a plurality of a data line115, a source electrode141, a channel layer131and a drain electrode143as shown inFIGS. 4 and 5. The data lines115are extended in a substantially column direction D2indicated inFIG. 5, and disposed on the gate insulation layer121. The source electrode141is extended from the data line115at a crossing area of the gate line111and the data line115, and overlaps with a portion of the gate electrode112as shown inFIGS. 4 and 5. A first portion of the drain electrode143is disposed on and overlapping the gate electrode112at an area overlapping with the source electrode141, and a second portion of the drain electrode143is extended toward and completely overlapped by the unit pixel area PA01.

Referring toFIGS. 1 and 5, a pair of adjacent gate lines111and a pair of adjacent data lines115intersect each other to define a substantially rectangular area therebetween, and the first and second pixel electrodes162and164are disposed on the rectangular shaped area. An entire of both of the first and second electrodes162and164may be disposed between the pair of adjacent gate lines111and the pair of adjacent data lines115. In the illustrated exemplary embodiment, the rectangular area will be defined as the unit pixel area PA01, but the invention is not limited thereto. Alternatively, a shape of the unit pixel area PA01may be a different shape, such as Z-shape, and/or may not be defined by gate lines111and data lines115.

Referring again toFIGS. 4 and 5, the gate electrode112, the gate insulation layer121, the channel layer131, the source electrode141and the drain electrode143define the first switching elements122, and form a three terminal element. The second switching element124may include a gate electrode114, the gate insulation layer121, the channel layer131, a source electrode142and a drain electrode144.

As shown inFIG. 4, the passivation layer151covering (e.g., overlapping) the data line115is disposed on the lower base substrate110, and an organic insulation layer153is disposed on the passivation layer151. A contact hole exposing a portion of the drain electrode143is extended through both the organic insulation layer153and the passivation layer151.

An optically transparent and electrically conductive material layer, such as indium tin oxide (“ITO”), indium zinc oxide (“IZO”), amorphous indium tin oxide (“a-ITO”), etc., is disposed on the organic insulation layer153, such as by a coating method. The optically transparent and electrically conductive material layer contacts with the drain electrode143through the contact hole. The optically transparent and electrically conductive material layer disposed on the organic insulation layer153is etched to form the first and second pixel electrodes162and164as shown inFIGS. 4 and 6. In the illustrated embodiment, in order to enhance a viewing angle, a viewing enhancing technology may be employed in the forming of the first and second pixel electrodes162and164. In one exemplary, a technology in which an alignment direction of liquid crystal is divided into a plurality of domains that are different from each other may be employed to the unit pixel area PA01.

Referring to the illustrated exemplary embodiment inFIGS. 1 and 6, in order to obtain the domains, the first and second pixel electrodes162and164may include a plurality of supporting electrodes163and167, and a plurality of micro slit portions161and165, respectively. The supporting electrodes163and167may have substantially a bar shape. The supporting electrodes163and167may be disposed in a crossed shape defined by the row direction D1and the column direction D2, for each of the first and second pixel electrodes162and164, respectively.

Each of the supporting electrodes163and167may include a first portion longitudinally extending in the row direction D1, and a second portion longitudinally extending tin the column direction D2. The first and second portions of each of the first and second pixel electrodes162and164may intersect each other at substantially a 90 degree angle, but the invention is not limited thereto.

Each of the micro slit portions161and165may be respectively extended along a first oblique line direction D3(FIGS. 1 and 5) and a second oblique line direction D4(FIGS. 1 and 5), which each cross the row direction D3and the column direction D2with an angle of about 45 degrees, respectively. Each of the micro slit portions161and165may be formed to extend in different directions by domains be employed to the unit pixel area PA01.

Each of the micro slit portion161and165longitudinally extend obliquely with respect to the first and second portions of the supporting electrodes163and167. In the plan view ofFIG. 6, boundaries or edges of the first and second pixel electrodes162and164defined by distal ends of the supporting electrodes163and167and the micro slit portion161and165define a substantially rectilinear shape.

Referring toFIGS. 1,4,5and6, the first pixel electrode162may include a first connecting electrode portion166protruded from a group of micro slit portions161and overlapping the contact hole extended through both the organic insulation layer153and the passivation layer151which exposes the portion of the drain electrode143of the first switching element122. The first connecting electrode portion166has a plan view dimension that is larger than both the micro slit portion161and the supporting electrode163portions. The first connecting electrode portion166, the micro slit portion161and the supporting electrode163portions are electrically connected to each other and disposed as a single, continuous and indivisible member in the unit pixel area PA01.

Referring toFIGS. 1,4,5and6, the second pixel electrode164may include a second connecting electrode portion169protruded from a group of micro slit portions165. A first end of the second connecting electrode portion169is continuously disposed with distal ends of the group of micro slit portions165from which it extends. The second connecting electrode portion169is longitudinally extended from the group of micro slit portions165in the column direction D2, and substantially parallel with the data lines115. The second connecting electrode portion169is disposed between a data line115and an adjacent border of the first pixel electrode162, as illustrated in the plan view ofFIGS. 1 and 6.

Referring toFIGS. 1,4,5and6, the second pixel electrode164may further include a third connecting electrode portion168protruded from a second (e.g., distal) end of the second connecting electrode portion169, and overlapping a contact hole extended through both the organic insulation layer153and the passivation layer151which exposes the portion of the drain electrode144of the second switching element124. The second connecting electrode portion169, the third connecting electrode portion168, the micro slit portion165and the supporting electrode167portions are electrically connected to each other and disposed as a single, continuous and indivisible member in the unit pixel area PA01.

A long axis of the liquid crystal may be arranged substantially in parallel with an extended direction of the micro slit portions161and165. As a result, a plurality of domains is formed to enhance a viewing angle of the LCD device. A lower polarizing plate (not shown) may be attached at a rear surface (e.g., a lowermost surface inFIG. 4) of the lower base substrate110.

In one exemplary embodiment, the micro slit portions161and165disposed through the first and second pixel electrodes162and164may be obliquely extended in a direction forming at an angle of about 45 degrees or about 135 degrees with respect to a lower polarizing axis of the lower polarizing plate, such as the first oblique line direction D3and the second oblique line direction D4.

FIG. 7is a cross-sectional view illustrating an exemplary embodiment of a process for manufacturing a lower alignment layer171on an array substrate101ofFIG. 4.

Referring toFIG. 7, the lower alignment layer171covering the first and second pixel electrodes162and164is formed (step S10). The lower alignment layer171is disposed overlapping and directly contacting each of the first and second pixel electrodes162and164, and the organic insulating layer153.

In an exemplary embodiment, the lower alignment layer171may be formed by coating a photo-reactive polymer of a cinematic series, and a polymer blend of a polyimide series on the first and second pixel electrodes162and164and curing the coated photo-reactive polymer and the polymer blend. In one exemplary embodiment, the photo-reactive polymer of a cinematic series and the polymer blend of a polyimide series are blended in a ratio of about 1:9 (weight percent) to 9:1 (weight percent) to melt in an organic solvent, and then the polymer melted in the organic solvent is coated on the substrate, such as in a spin coating method. The coated polymer is cured, such as by heating, so that the lower alignment layer171may be formed.

An ultraviolet (“UV”) light is irradiated on the lower alignment171to generate an alignment force characteristic for a liquid crystal layer180. By using the light alignment process, the lower alignment layer171may align liquid crystal of the liquid crystal layer180substantially in a vertical direction, that is, a direction from the array substrate101to the opposite substrate201which is substantially perpendicular to both the array substrate101to the opposite substrate201.

FIG. 8is a process diagram illustrating an exemplary embodiment of a process for manufacturing a lower RM layer190on the lower alignment layer171through a spray method.FIG. 9is a process diagram illustrating an exemplary embodiment of a process for manufacturing a lower RM layer190on the lower alignment layer171through a coating method.FIG. 10is a cross-sectional view illustrating another exemplary embodiment of a process for manufacturing a lower RM layer190on a lower alignment layer171.

Referring toFIG. 3, the lower RM layer190is formed on the lower alignment layer171(step S20). The lower RM layer190may be used to enhance a response speed of the LCD device by allowing a pretilt angle to the liquid crystal layer180. A term of the “mesogen” is used to define a light bridge high-molecular copolymer polymer including a mesogen group of a liquid crystal property. When a polarized UV light is irradiated to the mesogen, anisotropy of the mesogen is induced, and then a heat process is performed to enhance a direction property of liquid crystal.

In the illustrated embodiment, the mesogen group is a polymer material which has a liquid crystal property at a predetermined temperature range or a liquid solution state. The reactive mesogen RM may include a material or compound including one or more rod-shaped, banana-shaped, board-shaped or disk-shaped mesogenic groups, i.e. groups capable of showing liquid crystal phase behavior. The RM may include mesogen having acrylate, metacrylate, epoxy, oxetanes, vinyl ether, styrene, thiophene, etc.

In one illustrated exemplary embodiment, the mesogen blend RM01including the RM may be coated on the lower alignment layer171through a spray method using a spray nozzle SP01as shown inFIG. 8. Alternatively, as shown inFIG. 9, the mesogen blend RM01may be coated on the lower alignment layer171through a spin coating method using a coating nozzle NZ01. The mesogen blend RM01may include a free radical initiator having photosensitivity or heat sensitivity, and/or a polymer initiator such as a cationic agent. The initiator may be operated by light or heat. The mesogen blend RM01may include a composition such as at least one of polymer initiators.

After the mesogen blend RM01is applied to the lower alignment layer171(FIGS. 8 and 9), a volatile composition is removed from the mesogen blend RM01, and the lower RM layer190is formed on the lower alignment layer171as shown inFIG. 10. The lower RM layer190may be disposed on essentially a whole of the array substrate101, and overlapping and directly contacting the organic insulating layer153.

When liquid crystal is arranged on the lower alignment layer171, the lower RM layer190is aligned in an alignment direction of the lower alignment layer171to induce the liquid crystal to have a pretilt angle. In order not to cure the lower RM layer190, an incident light provided from an external side may be blocked to the lower RM layer190during the spray process or the spin coating process.

FIG. 11is a cross-sectional view illustrating an exemplary embodiment of a process for manufacturing a diffusion stop layer on a surface of a lower RM layer190.

In the method of manufacturing the LCD device, a liquid crystal layer180is disposed on the lower RM layer190. Since the lower RM layer190is not cured when the liquid crystal layer180is disposed on the lower RM layer, the RM in the lower RM layer190may be distributed to the liquid crystal layer180. When an amount of RM mixed to the liquid crystal layer180is relatively large, a generation of an undesirable afterimage may be increased in an LCD device. Referring toFIG. 11, a diffusion stop layer (not shown) may be formed on the lower RM layer190, in order to suppress the RM in the lower RM layer190from being transferred into the liquid crystal layer180. In an exemplary embodiment, the diffusion stop layer is a relatively thin film into which characteristics of a surface of the lower RM layer190are varied. The diffusion stop layer is disposed between the lower RM layer190and the liquid crystal layer180.

In one exemplary embodiment, a UV light of which strength and time are properly controlled, is irradiated to a surface of the lower RM layer190(as indicated by H01inFIG. 11) to soft light cure the surface of the lower RM layer190, so that the diffusion stop layer may be formed. Alternatively, an infrared ray of which strength and time are properly controlled is irradiated to a surface of the lower RM layer190to soft heat cure the surface of the lower RM layer190, so that the diffusion stop layer may be formed.

In an alternative embodiment, when adhesive characteristics between the lower RM layer190and the lower alignment layer171, and chemical composition of the RM are properly controlled and selected, the amount of the RM disposed in the liquid crystal layer180may be decreased even though the diffusion strop layer is not formed. Therefore, a formation process of the diffusion stop layer may be omitted.

FIG. 12is a cross-sectional view illustrating an exemplary embodiment of a process for disposing a liquid crystal layer180on a lower RM layer190.

A liquid crystal layer180is disposed on the lower RM layer190as shown inFIG. 12, after the formation process of the diffusion stop layer or after the formation process of the lower RM layer190(step S30). Liquid crystals181are disposed on the lower RM layer190, such as through a direct drop method, so that the liquid crystal layer180may be disposed on the lower RM layer190.

FIG. 13is a cross-sectional view illustrating an exemplary embodiment of a process for combining an array substrate101including a liquid crystal layer180disposed thereon, and an opposite substrate201.

As shown inFIG. 13, the opposite substrate201is combined with the array substrate101(step S40).

The opposite substrate201may include an upper base substrate210, a light-blocking pattern221, a color filter pattern231, an overcoating layer241, a common electrode251and an upper alignment layer261.

The light-blocking pattern221is disposed on the upper base substrate210in correspondence with (e.g., overlapped with portions of) the gate line111, the data line115, the first and second switching elements122and124and the storage line116. The light-blocking pattern221may a not be disposed overlapping the unit pixel area PA01. The color filter pattern231is disposed on the unit pixel area PA01which is not blocked by light. In an exemplary embodiment, the color filter pattern231may include, but is not limited to, a red color filter, a green color filter and a blue color filter. The red, green and blue color filters may be sequentially disposed in correspondence with each unit pixel area PA01in a column direction D1.

The overcoating layer241overlaps the color filter pattern231and the light-blocking pattern221, such being disposed on an entire of the upper base substrate210. The common electrode251is disposed on the overcoating layer241and opposite to the upper base substrate210with respect to the overcoating layer241. In the illustrated embodiment, a material of the common electrode251is same as that of the first and second pixel electrodes162and164.

Where the common electrode251is disposed corresponding substantially to the unit pixel area PA01, the common electrode251may be formed in a substantially flat plate shape in which slit portions, that is, an opening is not formed. The common electrode251may be disposed as a single, continuous and indivisible member as including no openings. In the illustrated embodiment, when micro slit portions161and165are formed in the first and second pixel electrodes162and164, respectively, and the common electrode251is formed in a substantially continuous flat plate shape in which slit portions are not formed, a liquid crystal cell type is called as a super-vertical alignment (“S-VA”) mode. Alternatively, the liquid crystal layer180may be driven in a pattern vertical alignment (“PVA”) mode. In the PVA mode, a plurality of slit portions for forming a fringe field on each of the first pixel electrode162, the second pixel electrode164and the common electrode251may be disposed.

Referring again toFIG. 13, the upper alignment layer261is disposed on the common electrode251. In an exemplary embodiment, a material of the upper alignment layer261is same as that of the lower alignment layer171.

An upper RM layer290may be disposed on the upper alignment layer261by using the same method if forming the lower RM layer190, that is, the spray method or the coating method as described above.

In an exemplary embodiment, an upper polarizing plate (not shown) may be disposed on an outer surface of the opposite substrate201, such as to form an outermost layer of the LCD device. A polarizing axis of the upper polarizing plate may be substantially perpendicular to that of the lower polarizing plate.

Prior to applying an electric field between the first and second pixel electrodes162and164of the array substrate101, and the common electrode251of the opposite substrate201, a long axis direction of liquid crystal181(hereinafter, referred to as a director of liquid crystal) may be aligned in a direction substantially perpendicular to the array substrate101and the opposite substrate201as shown inFIG. 13.

FIGS. 14 and 15are cross-sectional views illustrating an exemplary embodiment of a process for allowing a pretilt angle of liquid crystal molecules181.

Referring toFIGS. 14 and 15, light7is irradiated to the liquid crystal layer180through the opposite substrate201to affect a pretilt angle to the liquid crystal181at a surface of the lower RM layer190and a surface of the upper RM layer290(step S50).

When the pixel voltage is applied to the first and second pixel electrodes162and164, and when the common voltage is applied to the common electrode251, the director of the liquid crystal181is aligned in substantially a horizontal direction as shown inFIG. 14. Thus, a white driving mode may be realized. In exemplary embodiments, in order to fully align the director of the liquid crystal181, the pixel voltage and the common voltage may be increased.

In the white driving mode, as shown inFIG. 14, an ultraviolet light7is irradiated on the opposite substrate201. The lower RM layer190and the upper RM layer290are cured at surfaces of the lower RM layer190and the upper RM layer290adjacent to the lower and upper alignment layers171and261, respectively, to determine a direction property of liquid crystal181in response to the ultraviolet light.

Referring toFIG. 15, the liquid crystals181aand181bdirectly adjacent to the lower and upper RM layers190and290, respectively, may be substantially fixed in a direction in which the liquid crystals181aand181bare arranged in the horizontal direction. When an electric field is not applied to the liquid crystal layer180, as shown inFIG. 15, liquid crystals are arranged. That is, liquid crystals181aand181bhorizontally lie down at surfaces of the lower RM layer190and the upper RM layer290adjacent to the liquid crystal layer180, or have an inclined angle with respect to surfaces of the lower RM layer190and the upper RM layer290. For the liquid crystals located closer to a middle of liquid crystal layer between the array substrate101and the opposite substrate201, the liquid crystals181care gradually arranged substantially perpendicular with respect to surfaces of the lower RM layer190and the upper RM layer290as a distance increases from the array substrate101and the opposite substrate201.

Due to the arrangement of the liquid crystal181, a response time of the liquid crystal181may be advantageously enhanced. Moreover, arrangement directions of the liquid crystal are various, so that a viewing angle may be advantageously enhanced.

In the illustrated embodiment, the RM of the lower and upper RM layers190and290are not mixed with the liquid crystal181to be cured through a UV light, at a condition in which the RM is coated on surfaces of the lower alignment layer171and the upper alignment layer261. Advantageously, as described above, the RM is not mixed with the liquid crystal layer180.

FIG. 16is a cross-sectional view illustrating an exemplary embodiment of a generation of a remaining reactive mesogen layer in the LCD device which liquid crystals and reactive mesogen material are blended to form a liquid crystal layer580. inFIG. 16, a hatched pattern represents a liquid crystal molecule, and a non-hatched pattern represents a reactive mesogen.

Referring toFIG. 16, different from the previously illustrated embodiment, instead of forming a RM layer by coating the reactive mesogen on a lower alignment layer571and an upper alignment layer661, a light curing process may be performed at a mixture state of the RM into the liquid crystal layer580. The light curing method for the RM will be designated as a “blend method,” and the light curing method for the RM such as described for the previously illustrated embodiment will be designated as a “coating method” or “deposition method.”

According to the blend method, as shown inFIG. 16, the reactive mesogen RM04disposed at a relatively far distance from the lower alignment layer571and the upper alignment layer661is influenced by the lower alignment layer571and the upper alignment layer661, rather than reactive mesogens RM02and RM03adjacent to and disposed closer to the lower alignment layer571and the upper alignment layer661, respectively. In a manufacturing process, the adjacent reactive mesogens RM02and RM03are cured at a surface of the lower alignment layer571and the upper alignment layer661to form a lower RM layer590and an upper RM layer690, respectively. However, the reactive mesogen RM04disposed further from the lower alignment layer571and the upper alignment layer661is not cured, and remains in the liquid crystal layer580.

An undesirable decreasing amount of liquid crystal alignment capability due to the remaining reactive mesogen RM04in the liquid crystal layer580, is called as an alignment losing ratio. The alignment losing ratio depends upon not only characteristics of liquid crystal composition such as elasticity and viscosity, but also depends upon a chemical composition of the lower alignment layer571and the upper alignment layer661, and characteristics of pattern formed on an alignment layer.

FIG. 17is a graph illustrating a relationship between an amount of the RM which is remaining in the liquid crystal layer580of the LCD device as described inFIG. 16(blend method) and an exposing time, and an amount of the RM which is remaining in the liquid crystal layer of the LCD device as described inFIGS. 1 to 15(deposition method) and an exposing time.

InFIG. 17, a horizontal axis represents an exposing strength (J/cm2) of a UV light used to a light curing process for the RM, and a vertical axis represents a mass ratio of RM amount which is not cured after a light curing process and remains within the liquid crystal layer580with respect to a mass of an initially inputted RM. The RM remaining amount corresponding to the blend method (FIG. 16) is based on an amount of mixture RM of the liquid crystal layer580, and the RM remaining amount corresponding to a coating method (FIGS. 1-15) is based on an amount of RM included in the lower RM layer190and the upper RM layer290.

As shown inFIG. 17, observing the graph of the RM remaining amount of the blend method ofFIG. 16, the RM remaining amount is gradually decreased as a time increases, such as shown that the RM remaining amount is close to about 35 weight percent (wt %). That is, even though an exposing time is relatively long, it is recognized the RM remaining amount decreases close to a uniform threshold value, that is, the RM remaining amount does not continuously decrease.

When observing the graph of RM remaining amount of a coating method ofFIGS. 7-15, the RM remaining amount is about 15 wt % initially, and it is shown that the RM remaining amount is maintained to be about 12 wt % after the coating process is completed. That is, the RM is diffused into the liquid crystal layer180through the coating method, however, the RM remaining amount is about ⅓ of the blend method. Thus, in the coating method, the decreasing of display quality due to the remaining reactive mesogen RM04may be reduced or effectively prevented since the RM remaining amount is about ⅓ of the blend method.

An LCD structure including a remaining amount of reactive mesogen in the liquid crystal layer may be formed using an exemplary embodiment of the light curing method for the RM, designated as a “blend method,” and an exemplary embodiments of the light curing method for the RM designated as a “coating method” or “deposition method.” The remaining amount of reactive mesogen in the liquid crystal layer is considered as a distinctive structural characteristic of the LCD.

Since the remaining amount of reactive mesogen in the liquid crystal layer is imparted by forming a reactive mesogen layer on an alignment layer of a first substrate, disposing a liquid crystal layer on the lower alignment layer, combining the first substrate with a second substrate and irradiating the combined substrates to generate a pretilt angle in the liquid crystal layer of the coating method, such a process is considered as imparting the distinct structural characteristic of the remaining amount of reactive mesogen in the liquid crystal layer. Additionally, since the remaining amount of reactive mesogen in the liquid crystal layer is imparted by form a reactive mesogen layer through coating a mixture of the reactive mesogen and liquid crystal on a lower alignment layer and an upper alignment layer, and light curing the mixture state of the RM into the liquid crystal layer, such a process is also considered as imparting the distinct structural characteristic of the remaining amount of reactive mesogen in the liquid crystal layer.

FIGS. 18A and 18Bare cross-sectional views illustrating an exemplary embodiment of a pretilt angle of liquid crystal molecules at a black driving area B01and a white driving area W01, of an LCD device manufactured by the blending method as described inFIG. 16.

Referring toFIGS. 18A and 18B, the liquid crystal581is substantially vertically aligned and backlight (indicated by the upward arrows) is blocked at a black driving area B01of the LCD device manufactured by the blend method, so that black is displayed. The liquid crystal581is substantially horizontally aligned and backlight is transmitted at a white driving area W01of the LCD device manufactured by the blend method, so that white is displayed. In the blend method, the remaining RM RM04of the liquid crystal layer580responds to the backlight BL01during the black driving and the white driving, and then the remaining RM RM04is additionally cured at a surface of the lower RM layer590and the upper RM layer690. Accordingly, a pretilt angle of the liquid crystal581is altered at a surface of the lower RM layer590and the upper RM layer690.

Additional curing amounts of the RM are different from each other at the black driving area B01and the white driving area W01. Thus, as shown inFIG. 18B, when an electric field is turned off, that is, even though a total display screen is displayed in black, pretilt angles of the liquid crystal581may be different from each other at the black driving area B01and areas which were the white driving area W01.

FIGS. 19A and 19Bare photographs illustrating an exemplary embodiment of a display screen of the LCD device manufactured by the blending method as described inFIG. 16.FIG. 19Ashows a display screen that is observed when a total display screen is displayed in black after the white driving area W01is driven in about 220-gray with respect to the black driving area B01for about 24 hours at a peripheral temperature of about 50 Celsius degrees.FIG. 19Bshows a display screen that is observed when a total display screen is displayed in black after the white driving area W01is driven in about 245-gray with respect to the black driving area B01for about 168 hours at a peripheral temperature of about 50 Celsius degrees.

Referring toFIGS. 19A and 19B, in the aforementioned blend method, pretilt angles of the liquid crystal581are different from each other in accordance with the black driving area B01and the white driving area W01, so that a gradation displayed at a black status may be different from each other in accordance with areas and lapse time. Therefore, an undesirable afterimage may be clearly observed on the display screen. That is, display quality may be greatly decreased.

FIGS. 20A and 20Bare photographs illustrating a display screen of the LCD device as described inFIGS. 1 to 15.FIG. 20Ashows a display screen that is observed when a total display screen is displayed in black after the white driving area W01is driven in about 90-gray with respect to the black driving area B01for about 24 hours at a peripheral temperature of about 50 Celsius degrees.FIG. 20Bshows a display screen that is observed when a total display screen is displayed in black after the white driving area W01is driven in about 180-gray to about 200-gray with respect to the black driving area B01for about 168 hours at a peripheral temperature of about 50 Celsius degrees.

Referring toFIGS. 20A and 20B, the remaining RM RM04within the liquid crystal layer180is decreased in a coating method such as the present embodiment, so that an additional curing of the reactive mesogen due to the backlight BL01at the black driving area B01and the white driving area W01while an LCD device is driven is not generated. Thus, the pretilt angle of the liquid crystal181may be uniform in accordance with areas. As a result, it is recognized that an afterimage is not viewed even though a lapse time is about 168 hours as shown inFIG. 20B.

According to exemplary embodiment of an LCD device and a method of manufacturing the LCD device, in an LCD device which allows a pretilt angle by using a reactive mesogen, the remaining reactive mesogen remaining within a liquid crystal layer may be decreased. Advantageously, an afterimage due to the remaining reactive mesogen in a display screen may be removed, so that display quality may be enhanced. Therefore, the illustrated embodiments may be adapted to an LCD device using a reactive mesogen.