Liquid crystal display apparatus

A liquid crystal display (LCD) apparatus includes a first substrate including a switching element and a pixel electrode, the pixel electrode electrically connected to the switching element, and a second substrate disposed over the first substrate, the second substrate including a common electrode having a first slit and a second slit, wherein the first slit divides a unit pixel area into a plurality of domains, and the second slit partially overlaps the pixel electrode and is disposed to correspond to a boundary area of adjacent unit pixel areas.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 2008-122524, filed on Dec. 4, 2008, the contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to a liquid crystal display (LCD) apparatus, and more particularly, to an LCD apparatus including an electrode having a slit therethrough.

2. Discussion of the Related Art

A liquid crystal display (LCD) apparatus includes two display plates having field generating electrodes such as a pixel electrode and a common electrode thereon. A liquid crystal layer is disposed between the two display plates. Polarizing plates are respectively disposed on the outer surfaces of the two display plates. Voltages are applied to the field generating electrodes, so that an electric field may be generated in the liquid crystal layer. Thus, an arrangement direction of liquid crystal molecules in the liquid crystal layer is determined. As such, the LCD apparatus may control light passing through the liquid crystal layer and an image may be displayed.

The LCD apparatus having a vertical alignment (VA) mode provides a large contrast ratio and a large reference side viewing angle. In the LCD apparatus having the VA mode, when the electric field is not applied to the liquid crystal layer, the longitudinal axes of the liquid crystal molecules are arranged substantially perpendicular to the display plates.

The VA mode includes a patterned vertical alignment (PVA) mode and a multi-domain vertical alignment (MVA) mode. To increase a side viewing angle, a slit can be formed on the field generating electrodes in the PVA mode or a protrusion can be formed on the field generating electrodes in the MVA mode. The slit and the protrusion determine the inclination direction of the liquid crystal molecules. Thus, the reference side viewing angle may be increased by disposing the slit and the protrusion in various configurations.

However, the slit and the protrusion decrease the transmittance of the LCD apparatus, and the liquid crystal molecules in a boundary area between the pixel electrodes are difficult to control. As such, the aperture ratio of a unit pixel area may be decreased. For example, in a normally black mode of the PVA mode, adjacent domains simultaneously affect the liquid crystal molecules disposed near the boundary area of the adjacent domains. As such, textures may be generated near the boundary area due to unstable liquid crystal molecules.

The textures cause optical defects such as stains and afterimages in a display screen. A response time may increase due to the textures. When the width of a light-blocking part is increased to cover the textures, the aperture ratio is decreased.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a liquid crystal display (LCD) apparatus comprises an array substrate including a first substrate, a signal line formed on the first substrate, a switching element connected to the signal line, and a pixel electrode connected to the switching element, a counter substrate including a second substrate disposed over the array substrate, the counter substrate including a common electrode formed on the second substrate, wherein the common electrode includes a domain division slit dividing a unit pixel area into a plurality of domains, and includes a transmittance improvement slit partially overlapping the pixel electrode and corresponding to a boundary area of adjacent unit pixel areas, and a liquid crystal layer disposed between the array substrate and the counter substrate.

The counter substrate may further comprise a light-blocking part overlapping the boundary area and the switching element.

An edge of the light-blocking part can be disposed between a first edge of the transmittance improvement slit overlapping the pixel electrode and an edge of the pixel electrode defining the boundary area.

When an electric field is applied to the liquid crystal layer, an arrangement direction of liquid crystal molecules adjacent to the first edge and an arrangement direction of liquid crystal molecules disposed between the first edge and the edge of the pixel electrode can be different from each other.

The first edge and the edge of the pixel electrode can be formed substantially parallel with each other.

The length of the transmittance improvement slit can be shorter than the width of the unit pixel area.

A second edge of the transmittance improvement slit can face the first edge and can be disposed in the boundary area.

A distance between the second edge and the edge of the pixel electrode can be no less than two times and no more than three times a distance between the array substrate and the counter substrate.

The domain division slit can be integrally formed with the transmittance improvement slit.

The domain division slit may extend along an imaginary central line of the unit pixel area substantially parallel with a first direction, and the transmittance improvement slit may extend along a second direction substantially perpendicular to the first direction.

The domain division slit and the transmittance improvement slit can be connected to each other in a T-shape.

The signal line may comprises a gate line disposed under the domain division slit, extending along the first direction, and connected to a gate electrode of the switching element, and a data line extending along the second direction and overlapping the transmittance improvement slit in the boundary area, the data line connected to a source electrode of the switching element.

A width of the light-blocking part is larger than a width of the boundary area.

The pixel electrode in a first unit pixel area can be connected to a drain electrode of the switching element in a second unit pixel area adjacent to the first unit pixel area.

The pixel electrode can be driven by a previous gate driving method.

Embossed notches or engraved notches can be formed on the edges of the domain division slit facing each other.

According to an exemplary embodiment of the present invention, a liquid crystal display (LCD) apparatus comprises a first substrate including a switching element and a pixel electrode, the pixel electrode electrically connected to the switching element, and a second substrate disposed over the first substrate, the second substrate including a common electrode having a first slit and a second slit, wherein the first slit divides a unit pixel area into a plurality of domains, and the second slit partially overlaps the pixel electrode and is disposed to correspond to a boundary area of adjacent unit pixel areas.

A length of the second slit can be shorter than a width of the unit pixel area.

The first slit can be integrally formed with the second slit.

The first slit and the second slit can be connected to each other in a T-shape.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein.

FIG. 1Ais a plan view illustrating a unit pixel area of a liquid crystal display (LCD) apparatus according to an exemplary embodiment of the present invention.FIG. 1Bis an enlarged plan view showing portion A01inFIG. 1Aaccording to an exemplary embodiment of the present invention.FIG. 2is a cross-sectional view taken along the line I-I′ inFIG. 1Aaccording to an exemplary embodiment of the present invention.

Referring toFIGS. 1A,1B and2, the LCD apparatus100includes an array substrate101, a counter substrate201and a liquid crystal layer103.

The array substrate101and the counter substrate201face each other and are attached to each other by sealing members having, for example, a frame shape. Liquid crystal can be injected into a space formed by the array substrate101, the counter substrate201and the sealing members, to form the liquid crystal layer103. The counter substrate201may be a color filter substrate. The array substrate101may be an active matrix substrate having thin-film transistors (TFTs).

The array substrate101may have a substantially rectangular shape. Thus, a first direction D01is substantially parallel with a transverse direction or a horizontal direction of the array substrate101. A second direction D02is substantially parallel with a longitudinal direction or a vertical direction of the array substrate101, so that the second direction D02may be substantially perpendicular to the first direction D01.

In an exemplary embodiment, a unit pixel area PA01of the array substrate101may have a rectangular shape. Referring toFIG. 1A, a first side of the unit pixel area PA01along the first direction D01is longer than a second side of the unit pixel area PA02along the second direction D02. When a side of a pixel along the first direction D01is longer than a side of the pixel along the second direction D02and silts are formed through a common electrode of the counter substrate201, the pixel may be referred to as a landscape patterned vertical alignment (PVA) mode pixel. The landscape PVA mode pixel may be applied to a display apparatus having a wide screen, such as a Global Positioning System (GPS) navigation device.

FIGS. 3A and 3Bare plan views illustrating a method of forming an LCD apparatus according to an exemplary embodiment of the present invention.

Referring toFIGS. 2 and 3A, the array substrate101may include a lower substrate110, signal lines, a switching element TFT01and a pixel electrode150.

In an exemplary embodiment, a gate metal layer is formed on the lower substrate110. The lower substrate110may comprise, for example, glass or plastic via a sputtering process. The gate metal layer is patterned via a photolithography process, so that a plurality of gate lines111extending along the first direction D01and a plurality of gate electrodes113are formed. Each of the gate lines111extends along an imaginary central line of the unit pixel area PA01. The gate electrode113protrudes from the gate line111along the first direction D01of the gate line111. A storage electrode115protrudes from the gate line111opposite to the gate electrode113. A pixel electrode150is disposed in the unit pixel area PA01. The unit pixel area PA01is an individual area unit in which the liquid crystal layer103is independently controlled.

A gate insulation layer117is formed on the gate line111. The gate insulation layer117may comprise insulation material such as, for example, silicon nitride or silicon oxide. An impure amorphous silicon layer and a pure amorphous silicon layer are formed on the gate insulation layer117. The impure amorphous silicon layer and the pure amorphous silicon layer are patterned via the photolithography process, so that a channel layer119is formed. The channel layer119is formed on the gate insulating layer117corresponding to the gate electrode113.

Then, source metal layers are formed on the gate insulation layer117and are patterned, so that a plurality of data lines121extending along the second direction D02, a plurality of source electrodes123respectively extending from the data lines121, and drain electrode125may be formed. The data lines121are formed in boundary areas BA01. The boundary areas BA01are positioned between the unit pixel areas PA01adjacent to each other, and can extend along the second direction D02.

A first end portion of the drain electrode125may be disposed on the channel layer119and may face the source electrode123in a first unit pixel area PA01. The drain electrode125extends toward a second unit pixel area PA01adjacent to the first unit pixel area PA01along the second direction D02. As such, a second end portion of the drain electrode125opposite to the first end portion may be disposed to correspond to the storage electrode115in the second unit pixel area PA01.

Then, the impure amorphous silicon layer of the channel layer119is partially removed to partially expose the pure amorphous silicon layer. Oxygen plasma treatments may be performed for stabilizing a surface of the exposed pure amorphous silicon layer according to an exemplary embodiment of the present invention.

The switching element TFT01is formed adjacent to the boundary area BA01. The switching element TFT01may include the gate electrode113, the channel layer119, the source electrode123and the drain electrode125. When gate control signals are applied to the gate electrode113through the gate line111, data signals applied to the source electrode123through the data line121are applied to the drain electrode125.

Then, a passivation layer130is formed on the lower substrate110on which the data line121is formed. An organic insulation layer140is formed on the passivation layer130. A contact hole141is formed through the organic insulation layer140and the passivation layer130to partially expose the drain electrode125.

Then, referring toFIGS. 2 and 3B, conductive transparent material such as, for example, indium tin oxide (ITO) or indium zinc oxide (IZO) may be formed on the organic insulation layer140to form a conductive transparent material layer. The conductive transparent material layer is patterned via the photolithography process, so that the pixel electrode150is formed in the unit pixel area PA01. The pixel electrode150is connected to the drain electrode125through the contact hole141. The pixel electrode150is not formed on the switching element TFT01. The pixel electrode150in the first unit pixel area PA01may be electrically connected to the drain electrode125in the second unit pixel area PA01adjacent to the first unit pixel area PA01, so that the pixel may be controlled by a previous gate method.

Referring toFIG. 2, a lower alignment layer160may be formed on the lower substrate110on which the pixel electrode150is formed. The lower alignment layer160may initially align the liquid crystal layer103.

FIG. 4is a cross-sectional view taken along the line II-II′ inFIG. 1Aaccording to an exemplary embodiment of the present invention.

Referring toFIGS. 2 and 4, the counter substrate201may include an upper substrate210, a light-blocking part220, a color filter230, an overcoat layer240, a common electrode250and an upper alignment layer260.

The upper substrate210faces the lower substrate110and may include substantially the same material as the lower substrate110, such as, for example, glass or plastic.

Referring toFIGS. 1A and 4, the light-blocking part220is formed on the upper substrate210corresponding to the switching element TFT01, the gate lines111and the data lines121. The light-blocking part220may comprise metallic material such as, for example, including chromium (Cr) or organic material. The width of the light-blocking part220may be larger than that of the gate line111and that of the data line121, so that the light-blocking part220may cover the boundary area BA01.

The color filter230is formed on the upper substrate210and is partially exposed by the light-blocking part220. The color filter230may include one of red, green and blue color filters.

The overcoat layer240is formed on the color filters230and the light-blocking part220for planarization. Then, the conductive transparent material such as ITO or IZO may be formed on the overcoat layer240to form the conductive transparent material layer. The conductive transparent material layer is patterned via the photolithography process so that the common electrode250is formed. A domain division slit251and a transmittance improvement slit253are formed through the common electrode250via the photolithography process. The upper alignment layer260is formed on the common electrode250.

The domain division slit251is disposed over the gate line111and extends along the second direction D02. The domain division slit251divides the unit pixel area PA01into an upper domain and a lower domain. Embossed notches and engraved notches may be formed on the edges257of the domain division slit251facing each other.

The transmittance improvement slit253corresponds to the boundary area BA01and extends along the second direction D02. In an exemplary embodiment, the transmittance improvement slit253may completely overlap the data line121, and may partially overlap the pixel electrode150. The transmittance improvement slit253is shorter than the unit pixel area PA01along the second direction D02. Thus, the domain division slit251and the transmittance improvement slit253are connected to each other as, for example, a T-shape.

A first edge255is an edge of the transmittance improvement slit253overlapping the pixel electrode150. A second edge256is defined as an edge of the transmittance improvement slit253facing the first edge255and disposed in the boundary area BA01.

Referring toFIGS. 1A and 1B, the first edge255and an edge155of the pixel electrode150adjacent to the first edge255are parallel with each other. Referring toFIG. 4, the edge155of the pixel electrode150is closer to the data line121than the first edge255. Thus, a fringe field can be formed adjacent to the boundary area BA01. For example, the fringe field may be bent from the edge155of the pixel electrode150toward the first edge255of the transmittance improvement slit253.

A distance between the second edge256and the edge155of the pixel electrode150may be no less than two times and no more than three times a distance between the array substrate and the counter substrate201according to an exemplary embodiment of the present invention. As such, the fringe field may be sufficiently bent.

FIG. 5is a diagram illustrating arrangement directions of liquid crystal molecules in a boundary area inFIG. 4according to an exemplary embodiment of the present invention.

Referring toFIGS. 1A,1B,4and5, when an electric field is not applied to the liquid crystal layer103, an arrangement direction of the liquid crystal molecules may be substantially perpendicular to the array substrate101. When the electric field is applied to the liquid crystal layer103by the pixel electrode150and the common electrode250, the arrangement direction of the liquid crystal molecules may be substantially parallel with the array substrate101.

The liquid crystal molecules disposed adjacent to the first edge255and disposed opposite to the edge155of the pixel electrode150with respect to the first edge255may be arranged along a first alignment direction D03. The first alignment direction D03may be substantially perpendicular to the edges257of the domain division slit251. The liquid crystal molecules disposed between the first edge255and the edge155of the pixel electrode150may be arranged along a second alignment direction D04due to the fringe field. The second alignment direction D04may cross the first direction D01, and may be substantially perpendicular to the first direction D01.

Thus, in the unit pixel area PA01adjacent to the boundary area BA01, a head portion of the liquid crystal aligned along the first alignment direction D03may follow a tail portion of the liquid crystal aligned along the second direction D02. For example, the liquid crystal molecules aligned along the first and the second alignment directions D03and D04may not collide with each other, and are continuously distributed between the first and the second alignment directions D03and D04. As such, the liquid crystal molecules adjacent to the boundary area BA01are controlled. Thus, in the unit pixel area PA01adjacent to the boundary area BA01, textures due to the liquid crystal molecules may be decreased, so that the light-blocking part220corresponding to the unit pixel area PA01adjacent to the boundary area BA01may be partially removed. As a result, the width of the light-blocking part220may be decreased, so that the transmittance of the LCD apparatus100may be increased.

The light-blocking part220has the width larger than that of the boundary area BA01. Referring toFIGS. 1B and 4, an edge of the light-blocking part220may be disposed substantially close to the first edge255or may be disposed between the first edge255and the edge155of the pixel electrode150.

FIG. 6is a plan view illustrating a unit pixel area of an LCD apparatus without a transmittance improvement slit.FIG. 7is a cross-sectional view taken along the line III-III′ inFIG. 6.FIG. 8is a diagram illustrating arrangement directions of liquid crystal molecules in a boundary area inFIG. 6.

Referring toFIGS. 6 and 7, the LCD apparatus400is substantially the same as the LCD apparatus100except for the transmittance improvement slit253removed from a common electrode550inFIG. 6. The LCD apparatus400does not include the transmittance improvement slit253, so that a fringe field may be bent from an edge455of a pixel electrode450to the common electrode550toward the outside of the unit pixel area PA01.

Referring toFIGS. 7 and 8, when the electric field is applied to a liquid crystal layer403, the arrangement direction of the liquid crystal molecules adjacent to the boundary area BA01may be changed. The liquid crystal molecules in the unit pixel area PA01adjacent to the edge455of the pixel electrode450may be arranged along the first alignment direction D03. The liquid crystal molecules in the fringe field may be arranged along a third alignment direction D05. The third alignment direction D05may be opposite to the second alignment direction D04.

Referring toFIG. 8, the head portion of the liquid crystal molecules along the first alignment direction and the head portions of the liquid crystal molecules along the third alignment direction may collide with each other. Thus, the textures may be generated adjacent to the edge455of the pixel electrode450. Therefore, the liquid crystal molecules adjacent to the edge455of the pixel electrode450or adjacent to the boundary area BA01may not be effectively controlled. Thus, a light-blocking part520overlaps the pixel electrode450by a first width W01to eliminate the textures. However, due to the extended light-blocking part520, the light transmittance of the LCD apparatus400may be decreased.

According to an exemplary embodiment, the liquid crystal molecules adjacent to the boundary area BA01may be effectively controlled due to the transmittance improvement slit253. Thus, the light-blocking part220of the LCD apparatus100described in connection withFIGS. 1 to 4may have the width smaller that that of the LCD apparatus400described in connection withFIGS. 6 to 8. When the transmittance improvement slit253is formed according to an exemplary embodiment of the present invention, textures due to the liquid crystal molecules may be decreased. As such, the light transmittance of the LCD may be increased. According to an exemplary embodiment, the light-blocking part220may be partially removed corresponding to the unit pixel area PA01adjacent to the boundary area BA01. As a result, the width of the light-blocking part220may be decreased by the first width W01, so that the transmittance of the LCD apparatus100may be increased. Thus, the textures may be decreased in the area adjacent to the boundary area BA01, so that the response time of the liquid crystal layer103may be decreased.

FIG. 9shows a unit pixel area of an LCD apparatus described in connection withFIGS. 1A to 5according to an exemplary embodiment of the present invention.FIG. 10shows the unit pixel area of an LCD apparatus described in connection withFIGS. 6 to 8.

Referring toFIG. 9, the liquid crystal molecules adjacent to the boundary area BA01are continuously arranged between the first and the second alignment directions D03and D04. As such, the liquid crystal molecules may not collide with each other. Thus, profiles of the unit pixel area PA01may be substantially clear and the generation of the textures is substantially minimized in the unit pixel area PA01adjacent to the boundary area BA01.

Referring toFIG. 10, the liquid crystal molecules adjacent to the boundary area BA01may collide with each other. Thus, in the LCD apparatus400, the profiles of the unit pixel area PA01may be unclear and the textures may be generated in the unit pixel area PA01adjacent to the boundary area BA01. For example, the textures may be considerably generated in the right and the left side areas of the unit pixel area PA01.

Compared to the LCD apparatus100described in connection withFIGS. 1A to 5and the LCD apparatus400described in connection withFIGS. 6 to 8with respect to an aperture ratio and light transmittance, the LCD apparatus100according to an exemplary embodiment has better display quality than the LCD apparatus400illustrated inFIGS. 6 to 8. For example, the unit pixel area PA01inFIG. 10has an aperture ratio of about 52.7%. The unit pixel area PA01inFIG. 9has an aperture ratio of about 57.2%. Thus, the aperture ratio is increased by about 4.5%. The unit pixel area PA01inFIG. 10has a transmittance of about 5.43%. The unit pixel area PA01inFIG. 9has a transmittance of about 5.76%. Thus, the transmittance is increased by about 0.33%.

FIGS. 11A,11B,11C and11D are voltage-time graphs obtained from an LCD apparatus described in connection withFIGS. 1A to 5. InFIGS. 11A to 11D, a horizontal axis indicates test times and a vertical axis indicates voltages reduced from the luminance of a display area of the LCD apparatus100.

The voltage-time graphs inFIGS. 11A to 11Dshow test results for the LCD apparatus100using voltage-time test equipment such as a BM7 apparatus. The BM7 apparatus can be used to test the hysteresis and slow response of a displayed image in the display area.

FIG. 11Aindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level0to gray level31.FIG. 11Bindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level15to gray level31.FIG. 11Cindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level47to gray level31.FIG. 11Dindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level63to gray level31.

Referring to the voltage-time graphs inFIGS. 11A to 11D, in the LCD apparatus100, voltage levels are instantly changed when the grayscale is increased or decreased. Thus, no considerable delay along a time axis occurs during the period between luminances corresponding to different grayscales, and the voltage levels are instantly changed.

FIGS. 12A,12B,12C and12D are voltage-time graphs obtained from an LCD apparatus described in connection withFIGS. 6 to 8.

The voltage-time graphs inFIGS. 12A to 12Dshow test results for the LCD apparatus400using voltage-time test equipment such as the BM7 apparatus.FIG. 12Aindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level0to gray level31.FIG. 12Bindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level15to gray level31.FIG. 12Cindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level47to gray level31.FIG. 12Dindicates a voltage-time relationship when the grayscale of the displayed image is changed from gray level63to gray level31.

Referring to the voltage-time graphs inFIGS. 12A to 12D, voltage levels are delayed with a time period when grayscale is increased or decreased. For example, substantial delays along the time axis occur during the period between the luminances corresponding to the different grayscales. As such, the response delay occurs when the grayscale is changed.

Thus, the response time and the transmittance in the LCD apparatus100may be improved with respect to the LCD apparatus400.

According to an exemplary embodiment of the present invention, a response time and transmittance in an LCD apparatus may be improved. Thus, the LCD apparatus according to an exemplary embodiment of the present invention may be used for an LCD apparatus including slits for forming a multi-domain structure.

According to an exemplary embodiment of the present invention, liquid crystal molecules adjacent to a boundary area may be effectively controlled, so that textures adjacent to the boundary area may be decreased. Thus, the width of a light-blocking part and a response time may be decreased. As a result, the transmittance of a unit pixel area may be increased, so that the display quality of the LCD apparatus may be increased.

Although exemplary embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present invention should not be limited thereto and that various other changes and modifications may be affected therein by one of ordinary skill in the related art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention.