Panel for a liquid crystal display and method of forming the same

A panel for a liquid crystal display including a substrate, and at least one spacer formed over the substrate. The at least one spacer has a tapered shape with an inclination angle in the range of about 20–about 70 degrees and a height in the range of about 2.5–about 5.0 microns.

BACKGROUND

(a) Technical Field

The present disclosure relates to a panel for a liquid crystal display, and in particular, to a liquid crystal display panel including spacers.

(b) Disclosure of Related Art

A conventional liquid crystal display (LCD) includes two panels in which at least one of the two panels is coated with an alignment layer and includes field-generating electrodes. A liquid crystal (LC) layer having dielectric anisotropy is filled in a gap (called a cell gap) between the panels. Electric fields are applied to the LC layer by the field-generating electrodes and the transmittance of light through the panels is controlled by adjusting the field strength, thereby displaying desired picture images.

The two panels are assembled by printing a sealant along a periphery of one of the panels and by hot-pressing the panels.

The cell gap is maintained by elastic spacers provided between the panels and spacers included in the sealant. The LC layer is encapsulated by the sealant. The spacers includes spherical spacers spread on the panels and columnar spacers formed by photolithography.

The columnar spacers are vertically compressed to support the panels. When the cross sections of the spacers are too small, the spacers are apt to be deformed or to be damaged due to large compression deformation. If the cross sections of the spacers are too large, it is difficult to adjust the amount of the LC material to be filled in the gap between the panels due to the small compression deformation of the spacers. The inappropriate amount of the LC causes bubbles or non-uniform distribution of the LC.

As LCDs are made larger, it becomes important to keep the cell gap uniform to facilitate proper formation of the LC layer.

SUMMARY OF THE INVENTION

A panel for a liquid crystal display according to an embodiment of the invention includes a substrate, and at least one spacer formed over the substrate. The at least one spacer has a tapered shape with an inclination angle in the range of about 20–about 70 degrees and a height in the range of about 2.5–about 5.0 microns.

A liquid crystal display according to embodiment of the invention includes a first panel, a second panel disposed opposite the first panel, and a liquid crystal layer and at least one spacer disposed between the first panel and the second panel. The spacer has a tapered shape with an inclination angle in the range of about 20–about 70 degrees and a height in the range of about 2.5–about 5.0 microns.

A method of forming a liquid crystal display according to an embodiment of the invention includes forming a thin film transistor array panel including a plurality of pixel electrodes, and forming a plurality of spacers over the thin film transistor array panel between the plurality of pixel electrodes. A common electrode panel is formed and a sealant is coated over at least one of the thin film transistor array panel and the common electrode panel. A liquid crystal layer is formed over the at least one of the thin film transistor array panel and the common electrode panel coated with the sealant. The thin film transistor array panel and the common electrode panel are adhered together to form a panel assembly, and the panel assembly is scribed to form a liquid crystal display.

In at least one embodiment of the invention, the spacers are located directly over the data lines.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, the thickness of layers, films and regions are exaggerated for clarity. Like numerals refer to like elements throughout.

A panel assembly for LCDs according to an embodiment of the present invention will be now described in detail with reference toFIGS. 1 and 2.

FIG. 1is a plan view of a panel assembly for LCDs according to an embodiment of the present invention andFIG. 2is a sectional view of the panel assembly shown inFIG. 1taken along the line II–II′.

As shown inFIGS. 1 and 2, a panel assembly120according to an embodiment of the present invention includes two panels10and20and a plurality of LC layers3, a plurality of sealants500, and a plurality of columnar spacers400, which are disposed between the two panels10and20.

The panel assembly120includes a plurality of, for example, four device areas divided by dotted lines A and B. The panel assembly120is separated into the respective LCDs by scribing the panel assembly120along the dotted lines A and B.

Each of the device areas (or an LCD) includes a display area101,102,103or104for displaying images. The display areas101–104are substantially enclosed by the sealant500, which also confines the LC layer3. The LC layer3may be formed after the panel assembly120is separated into the respective devices.

The spacers400are provided for maintaining a uniform gap between the panels10and20and the sealant500may contain spacers for supporting the panels10and20parallel to each other.

The spacers400have a compression deformation equal to or larger than about 0.40 microns in response to 5 gf and are compressed by about 0.2 microns. The concentration of the spacers400is preferably about 250–450/cm2.

A method of manufacturing the spacers shown inFIG. 2according to an embodiment of the present invention is described in detail with reference toFIGS. 3 and 4.

FIG. 3is a sectional view of a panel and a plurality of column spacers formed thereon for an LCD before panel combination according to an embodiment of the present invention.

Referring toFIG. 3, a negative acrylic photoresist (not shown) is coated on an LC panel10. An exposure mask (not shown) including an opaque film having a plurality of transmissive areas, such as openings, is disposed on the panel10. The photoresist is then exposed to light through the exposure mask and developed to form a plurality of spacers400at desired positions.

Each contact area between the spacer400and the panel10may be circular or tetragonal and has a magnitude preferably in a range of about 600 to 1,000 square microns. For a circular contact area, the diameter of the circle is preferably equal to about 28–38 microns.

The height of the spacers400is about 2.5–5.0 microns. The spacers400preferably have a tapered shape with an inclination angle θ of about 20–70 degrees.

The spacers400have optimal compression deformation and disperse the stress exerted on the panels10and20. The spacers400maintain a uniform cell gap between the two panels10and20and facilitate proper adjustment of an amount of LC for forming the liquid crystal layer3.

One of the panels10and20shown inFIGS. 1 and 2is a thin film transistor (TFT) array panel provided with a plurality of gate lines (not shown) and a plurality of data lines (not shown) for transmitting electrical signals such as scanning signals and data signals, a plurality of TFTs (not shown) electrically connected to the gate lines and the data lines for controlling the data signals, and a plurality of pixel electrodes (not shown) that receive the data voltages for driving the LC molecules.

The other of the panels10and20shown inFIGS. 1 and 2is provided with a common electrode (not shown) facing the above-described pixel electrodes to generate electric fields for driving the LC molecules, and a plurality of color filters (not shown) for color display. The colors represented by the color filters preferably include three primary colors, i.e., red, green and blue.

In other embodiments of the invention, the color filters and/or the common electrode may be formed on the TFT array panel and the common electrode on the TFT array panel may have a shape of a bar or a stripe.

FIG. 4shows locations of the spacers400shown inFIG. 2according to an exemplary embodiment of the present invention.

Referring toFIG. 4, a plurality of red, green and blue color filters R, G and B are arranged in a stripe type. The spacers400are arranged in a regular or periodic manner along a row direction and a column direction. For example, the spacers400are located between the blue filters B and the red filters R and spaced apart from each other by predetermined transverse and longitudinal distances as shown inFIG. 4. In particular, the spacers400are preferably located over the gate lines, the data lines, or the TFTs.

An LC panel assembly according to an exemplary embodiment of the present invention will be described in more detail with reference toFIGS. 5–7.

FIG. 5is a layout view of an LCD according to exemplary embodiments of the present invention,FIG. 6is a sectional view of the LCD shown inFIG. 5taken along the line VI–VI′ according to one exemplary embodiment of the invention, andFIG. 7is a sectional view of the LCD shown inFIG. 5taken along the line VI–VI′ according to another exemplary embodiment of the invention.

An LCD according to an embodiment of the present invention includes a TFT array panel100, a common electrode panel200, and a LC layer3and a plurality of column spacers400disposed between the panels100and200.

A plurality of gate lines121for transmitting gate signals and a plurality of storage electrode lines131are formed on an insulating substrate110.

The gate lines121and the storage electrode lines131extend substantially in a transverse direction and are separated from each other. A plurality of projections of each gate line121form a plurality of gate electrodes124. The storage electrode lines131are supplied with a predetermined voltage such as a common voltage, which is applied to a common electrode270on the common electrode panel200of the LCD.

The gate lines121and the storage electrode lines131may have a multi-layered structure including two films, a lower film (not shown) and an upper film (not shown), having different physical characteristics. The upper film is preferably made of low resistivity metal including an Al containing metal such as, for example, Al and Al alloy for reducing signal delay or voltage drop in the gate lines121and the storage electrode lines131. The lower film is preferably made of material such as, for example, Cr, Mo and Mo alloy, which has good contact characteristics with other materials such as indium tin oxide (ITO) or indium zinc oxide (IZO). An exemplary combination of the lower film material and the upper film material is Cr and Al—Nd alloy.

The lateral sides of the gate lines121and the storage electrode lines131are tapered, and the inclination angle of the lateral sides with respect to a surface of the substrate110is in a range of about 30–80 degrees.

A gate insulating layer140preferably made of silicon nitride (SiNx) is formed on the gate lines121and the storage electrode lines131.

A plurality of semiconductor islands150preferably made of hydrogenated amorphous silicon (abbreviated as “a-Si”) or polysilicon are formed on the gate insulating layer140. The semiconductor islands150are located opposite the respective gate electrodes124.

A plurality of ohmic contact islands163and165preferably made of silicide or n+ hydrogenated a-Si heavily doped with n type impurity are formed on the semiconductor islands150.

The lateral sides of the semiconductor islands150and the ohmic contacts163and165are tapered, and the inclination angles thereof are preferably in a range of about 30–80 degrees.

A plurality of data lines171and a plurality of drain electrodes175separated from each other are formed on the ohmic contacts163and165and the gate insulating layer140.

The data lines171for transmitting data voltages extend substantially in the longitudinal direction and intersect the gate lines121and the storage electrode lines131. A plurality of branches of each data line171, which project toward the drain electrodes175, form a plurality of source electrodes173. A source electrode173and a drain electrode175in a pair are separated from each other and opposite each other with respect to a gate electrode124. A gate electrode124, a source electrode173, and a drain electrode175along with the semiconductor island150form a TFT having a channel between the source electrode173and the drain electrode175.

The data lines171and the drain electrodes175may also include a lower film (not shown) preferably made of Mo, Mo alloy or Cr and an upper film (not shown) located thereon and preferably made of Al containing metal.

Like the gate lines121and the storage electrode lines131, the data lines171and the drain electrodes175have tapered lateral sides, and the inclination angles thereof are in the range of about 30–80 degrees.

The ohmic contacts163and165are interposed only between the underlying semiconductor islands150and the overlying source electrodes173and the overlying drain electrodes175thereon and reduce the contact resistance therebetween.

A passivation layer180is formed on the data lines171, the drain electrodes175, and exposed portions of the semiconductor islands150, which are not covered with the data lines171and the drain electrodes175. The passivation layer180is preferably made of photosensitive organic material having a good flatness characteristic, low dielectric insulating material such as a-Si:C:O and a-Si:O:F formed by plasma enhanced chemical vapor deposition (PECVD), or inorganic material such as silicon nitride and silicon oxide. The passivation layer180may have a double-layered structure including a lower inorganic film and an upper organic film for preventing direct contact between the semiconductor islands150and an organic film.

The passivation layer180has a plurality of contact holes182and185exposing end portions179of the data lines171and the drain electrodes175, respectively. The passivation layer180also has a plurality of contact holes181exposing end portions129of the gate lines121. The contact holes181,182and185can have various shapes such as, for example, a polygonal or circular shape. The area of each contact hole181,182or185is preferably equal to or larger than 0.5 mm×15 μm and not larger than 2 mm×60 μm. The sidewalls of the contact holes181,182and185are inclined with an angle of about 30–85 degrees or have stepwise profiles.

A plurality of pixel electrodes190and a plurality of contact assistants81and82, which are preferably made of ITO, IZO or Cr, are formed on the passivation layer180.

The pixel electrodes190are physically and electrically connected to the drain electrodes175through the contact holes185such that the pixel electrodes190receive the data voltages from the drain electrodes175. The pixel electrodes190supplied with the data voltages generate electric fields in cooperation with the common electrode270, which reorient liquid crystal molecules disposed therebetween.

A pixel electrode190and a common electrode270form a capacitor called a “liquid crystal capacitor,” which stores applied voltages after turn-off of the TFT. An additional capacitor called a “storage capacitor,” which is connected in parallel to the liquid crystal capacitor, is provided for enhancing the voltage storing capacity. The storage capacitors are implemented by overlapping the pixel electrodes190with the storage electrode lines131. The capacitances of the storage capacitors, i.e., the storage capacitances can be increased by providing a plurality of storage capacitor conductors, which are electrically connected to the pixel electrodes190, between the gate insulating layer140and the passivation layer180opposite the pixel electrodes190and the storage electrodes lines131.

The pixel electrodes190can overlap the data lines171to increase aperture ratio.

The contact assistants81and82are connected to the exposed end portions129of the gate lines121and the exposed end portions179of the data lines171through the contact holes181and182, respectively. The contact assistants81and82protect the exposed portions129and179and complement the adhesiveness of the exposed portions129and179and external devices.

Portions of the passivation layer180near the contact assistants81and82may be completely removed, and such a removal is particularly advantageous for a chip-on-glass type LCD.

A black matrix220for preventing light leakage is formed on an insulating substrate210, such as, for example, transparent glass. The black matrix220includes a plurality of openings facing the pixel electrodes190and having substantially the same shape as the pixel electrodes190.

A plurality of red, green and blue color filters230is formed substantially in the openings of the black matrix220. An exemplary arrangement of the color filters230is a stripe type arrangement in which each color filter230is arranged in a separate column.

A common electrode270preferably made of transparent conductive material such as ITO and IZO is formed on the color filters230and the black matrix220. The common electrode270covers the entire surface of the panel200.

The wider surfaces of the spacers400are in contact with the common electrode panel200as shown inFIG. 7or in contact with the TFT array panel100as shown inFIG. 6. AlthoughFIGS. 5–7show the spacers400located over the data lines171and a TFT, the spacers400can be located over the gate lines121, or any other area covered by the black matrix220.

A pair of polarizers (not shown) is provided on outer surfaces of the panels100and200.

The LCD may be, for example, a twisted nematic (TN) mode LCD where liquid crystal molecules in the liquid crystal layer3having positive dielectric anisotropy are aligned parallel to surfaces of the panels100and200and the molecular orientations are twisted from the surface of one of the panels100and200to the surface of the other of the panels100and200in the absence of an electric field. Alternatively, the LCD may be a vertically aligned (VA) mode LCD, that is, the liquid crystal molecules in the liquid crystal layer3with negative dielectric anisotropy are aligned vertical to surfaces of the panels100and200in the absence of an electric field. Alternatively, the LCD may be an optically compensated bend (OCB) mode LCD, where the liquid crystal molecules have a bend alignment symmetrical with respect to a mid-plane between the panels100and200in the absence of an electric field.

A method of manufacturing a panel assembly for an LCD according to an embodiment of the invention is now described in detail with reference toFIGS. 1 and 2as well asFIGS. 5 and 6.

Referring toFIGS. 5 and 6, a plurality of gate lines121, a plurality of data lines171, a plurality of TFTs, a plurality of pixel electrodes190and the like are formed on an insulating substrate110to form a TFT array panel100. An organic insulating material is deposited on the panel100and patterned by photolithography to form a plurality of spacers400between the pixel areas. A black matrix220, a plurality of red, green and blue color filters230, a common electrode270, and so on are formed on another substrate210to form a common electrode panel200. The size of the spacers400is preferably equal to about 110–130% of the distance between the panels100and200. The formation of the spacers400using photolithography enables uniform arrangement of the spacers400such that a thin uniform cell gap can be obtained throughout the panels100and200and prevents the spacers400from being placed on the pixel electrodes190, thereby improving display characteristics.

A sealant500is coated on one of the panels100and200as shown inFIGS. 1 and 2. The sealant500has a shape of a closed loop without an injection hole for injecting LC. The sealant500may be made of thermosetting material or ultraviolet-hardening material and may contain a plurality of ellipsoidal or spherical spacers for keeping the gap between the panels100and200. Since the sealant500has no injection hole, it is important to exactly control the amount of the LC material. To avoidan excessive amount of the LC or an insufficient amount of the LC, a buffer region without LC material is preferably provided at the sealant500. The sealant500preferably has an anti-reaction film on its surface, which does not react with the LC layer3.

LC material is coated or dropped using an LC coater on one of the panels100and200coated with the sealant500. The LC coater may have a dice shape such that it can drop the LC material at the LC device areas101–104. The LC may be sprayed on the entire surface of the LC device areas101–104. In this case, the LC coater has a shape of a sprayer.

The panels100and200are delivered to an assembly device having a vacuum chamber. The area surrounded by the panels100and200and the sealant500is evacuated and the panels100and200are closely adhered to each other using atmospheric pressure such that the distance between the panels100and200reaches a desired cell gap. The sealant500is completely hardened by illumination with an ultra-violet (UV) ray using a light exposer. In this way, the two panels100and200are assembled to form a panel assembly120. The two panels100and200are exactly aligned during the step of adhering the panels100and200and the step of illuminating the sealant500.

The panel assembly120is separated into the LC device areas101–104using a scribing machine.

While the present invention has been described in detail with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the sprit and scope of the appended claims.