Abstract:
A method of fabricating a transflective liquid crystal display device includes providing first and second substrates that include a plurality of unit pixels divided into a transmission part and a reflection part, forming a first color filter unit by applying a first color pigment in the transmission part of the first substrate, forming a second color filter unit by applying a transparent material and a second color pigment in the reflection part of the first substrate, and attaching the first substrate and a second substrate together.

Description:
The present invention claims the benefit of Korean Patent Application No. 28742/2002 filed in Korea on May 23, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device and method of fabricating a transflective liquid crystal display device. 
     2. Discussion of the Related Art 
     In general, display devices require low power consumption, high picture quality, thin profile, and light weight. Presently, liquid crystal display (LCD) devices are replacing conventional cathode ray tubes (CRTs). 
     In common liquid crystal display devices, an image is displayed by light radiated from a light source, i.e., a back-light device located on a lower part of a liquid crystal display panel. However, the amount of light actually transmitting through the liquid crystal display panel is about 7% of the light generated from the back-light device. Accordingly, a significant amount of the light produced by the back-light device is absorbed or blocked by the liquid crystal display panel. Thus, power consumption of the back-light is increased. 
     In order to solve the power consumption problem of the back-light device, reflective liquid crystal display devices that do not use the back-light device are being developed. These reflective liquid crystal display devices use natural light, thereby reducing power consumption of the back-light device, and thus allow portable use of the liquid crystal display devices. The reflective liquid crystal display devices make use of ambient light by reflecting the ambient light using an opaque material having reflective property within pixel areas of the liquid crystal display devices. 
     However, the ambient light is not always available. Accordingly, the reflective liquid crystal display devices can only be effectively used where an abundance of ambient light is available, and cannot be used in low light or dark environments. Thus, transflective liquid crystal display devices, which combine advantages of the reflective liquid crystal display devices using the natural light and of the transmission liquid crystal display devices using the back-light device, are being developed. The transflective liquid crystal display devices can be easily converted into reflection mode and transmission mode device by user selection. 
     In general, the transflective liquid crystal display devices simultaneously function like both the transmission mode liquid crystal display devices and the reflective mode liquid crystal display devices. Accordingly, the user may be able to use the light of the back-light device and the ambient light. Thus, operation of the transflective liquid crystal display devices is dictated or limited by environmental conditions, and the power consumption can be reduced. 
       FIG. 1  is a perspective view of a transflective liquid crystal display device according to the related art. In  FIG. 1 , a transflective liquid crystal display device comprises a color filter substrate  10  having a transparent common electrode  8  formed on a black matrix  6  and a color filter  7 , a pixel area P having a pixel electrode  18  divided into a transmission part  16  and a reflection part  17 , and an array substrate  20  having a switching device S and gate and data lines  13  and  14 . In addition, a liquid crystal material layer  30  is formed between the color filter substrate  10  and the array substrate  20 . 
       FIG. 2  is a partial cross sectional view of a transflective liquid crystal display device according to the related art. In  FIG. 2 , the array substrate  20  and the color filter substrate  10  having the switching device S and the color filter  7  on two transparent substrates  5  and  15  are disposed to face each other, respectively. In addition, the liquid crystal material layer  30  is formed between the array substrate  20  and the color filter substrate  10 . 
     The switching device S is formed on the array substrate  20  and is disposed in a pixel region for supplying and blocking a signal voltage to the liquid crystal material layer  30 . The switching device S includes a gate electrode  21  to which a scan signal is supplied, an active layer  23  having a semiconductor layer  23   a  activated in response to the scan signal to form a channel, and an n +  doped ohmic contact layer  23   b  that is formed on both sides of the semiconductor layer  23   a , a gate insulating layer  24  for electrically insulating the active layer  23  from the gate electrode  21 , a source electrode  24  formed on the active layer  23  to which a data signal is input, and a drain electrode  25  transmitting the data signal input to the source electrode  24  to the pixel electrode when the semiconductor layer  23   a  is activated. In addition, a passivation layer  26  is formed on an entire surface of the array substrate  20  for protecting the source electrode  24  and the drain electrode  25 . Moreover, a contact hole  29  is formed on the passivation layer  26  to electrically connect the drain electrode  25  to the pixel electrode  27 . 
     The black-matrix  6  is formed within an area of the color filter substrate  10  corresponding to the area where the switching device S is formed in order to block the light and prevent it from being transmitted into areas above the black matrix  6 . In addition, the pixel electrode  27 , which is connected to the drain electrode  25  through the contact hole  29 , is formed on the pixel region P (in  FIG. 1 ) except at the portion where the switching device S is formed, and a reflective electrode  28  made of a metal having high reflection properties is formed on the pixel electrode  27 . 
     A portion of the reflective electrode  28  is removed to form a transmitting portion  16  having a width t. As described above, the transmission part  16  is formed within the pixel region P, whereby the light input from a direction of the transparent substrate  5  is reflected by the reflection electrode  28  and emitted along the same direction of the transparent substrate  5  in the reflection mode. In addition, the light emitted from the back-light device adjacent to the transparent substrate  15  is transmitted through the transmission part  16  in the transmission mode to produce an image. 
     A concave recess portion is formed within the area where the transmission part  16  is formed by removing portions of the passivation layer  26  and the reflection electrode  28 . The transmission part  16  is formed to have a concave recess shape in order to match ON/OFF modes of the reflection part and the transmission part  16  and to maximize the efficiency of the transmission mode. In addition, it is desirable that a ratio between a cell gap d 2  of the transmission part  16  and a cell gap d 1  of the reflection part is to be 2:1, that is, d 2  is to be twice d 1 . Accordingly, the transmission efficiencies on the reflection part and on the transmission part  16  are theoretically the same. 
     However, in the transflective liquid crystal display device according to the related art, the switching device S formed on the array substrate  20  is adversely affected by the process of etching the passivation layer  26  on the array substrate  20 . Accordingly, inferiority of the switching device S may be generated. For example, the switching device S, the gate insulating layer  22 , the passivation layer  26 , and the transparent electrode  27  formed on the array substrate  20  are affected by the process of forming the step in the passivation layer  26 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a transflective liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a transflective liquid crystal display device having an optimal image property showing same color purity and transmission rate both in a reflection mode and in a transmission mode. 
     Another object of the present invention is to provide a transflective liquid crystal display device for preventing inferiority during fabrication processing and for simplifying fabrication processes. 
     Another object of the present invention is to provide a method for fabricating a transflective liquid crystal display device having an optimal image property and for preventing inferiority during fabrication processing. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, A method of fabricating a transflective liquid crystal display device includes providing first and second substrates that include a plurality of unit pixels divided into a transmission part and a reflection part, forming a first color filter unit by applying a first color pigment in the transmission part of the first substrate. forming a second color filter unit by applying a transparent material and a second color pigment in the reflection part of the first substrate, and attaching the first substrate and a second substrate together. 
     In another aspect, a method of fabricating a transflective liquid crystal display device includes providing first and second substrates that include a plurality of unit pixels divided into a transmission part and a reflection part, etching a portion of the transmission part of the first substrate to a predetermined thickness, forming a first color filter unit by applying a color pigment on the etched portion, forming a second color filter unit by applying the color pigment in the reflection part of the first substrate so that a first cell gap of the transmission part is larger than a second cell gap of the reflection part, forming a passivation layer on the second substrate, patterning a transparent electrode and a reflection electrode on the second substrate upon which the passivation layer is formed, and attaching the first substrate and the second substrate together. 
     In another aspect, a transflective liquid crystal display device includes first and second substrates that include a plurality of unit pixels which are divided into a transmission part and a reflection part, a color filter including a first color filter unit in the transmission part and a second color filter unit in the reflection part so that a first cell gap of the transmission part is larger than a second cell gap of the reflection part, a switching device on the second substrate, a passivation layer on an entire surface of the second substrate upon which the switching device is formed, a transparent electrode and a reflection electrode on the second substrate upon which the passivation layer is formed, and a liquid crystal material layer between the first substrate and the second substrate. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a perspective view of a transflective liquid crystal display device according to the related art; 
         FIG. 2  is a partial cross sectional view of a transflective liquid crystal display device according to the related art; 
         FIGS. 3A and 3B  are graphs showing transmittance versus wavelength of a red color filter according to the present invention; 
         FIG. 4  is a partial cross sectional view of an exemplary transflective liquid crystal display device according to the present invention; 
         FIGS. 5A through 5C  are cross sectional views of an exemplary fabrication process for color filters according to the present invention; 
         FIG. 6  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention; 
         FIG. 7  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention; and 
         FIG. 8  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIGS. 3A and 3B  are graphs showing transmittance versus wavelength of a red color filter according to the present invention. In  FIG. 3A , when light is transmitted through a red color filter having a discretionary thickness L, the light of wavelength band (F) corresponding to the red color has a transmittance of nearly 1. However, the complete absorption characteristic is not shown on the wavelength band (G) corresponding to other colors, i.e., the transmittance (H) larger than 0.1 is shown. Thus, the light corresponding to the wavelength band except the red color is also transmitted as mixed with the light corresponding to the wavelength band of the red color. 
     On the contrary, when the thickness of the red color filter is to be 2×L, the transmittance of the light corresponding to the red color wavelength band is hardly changed. However, the transmittance (I) of the light in the wavelength band of 500 to 560 nm is nearly 0, in FIG.  3 B. 
     As described above, the transmittance of the light transmitting the color filter is changed according to the thickness of the color filter. For the transmission mode in the transflective liquid crystal display device, the light emitted from a back-light device is viewed after passing through the color filter once. For the reflection mode, the light input through the color filter from an upper side into the liquid crystal display device is reflected on the reflection electrode and is viewed after passing through the color filter for a second time. Thus, the first light passing through the transmission part is colored once and the second light passing through the reflection part is colored twice, whereby different color purities are created for the first and second lights. For example, assuming that the thickness of the color filter is L, and that the transmittance characteristic in  FIG. 3A  is represented for the transmission mode and the transmittance characteristic in  FIG. 3B  is represented for the reflection mode, then there is a difference between the color purities. 
     To solve this problem, the color purity of the light passing through the transmission part can be made to be the same as that of the light passing the reflection part by putting more pigment in the color resin to differentiate the thickness of the color filter on the portion corresponding to the transmission part. For example, the thickness of the color filter corresponding to the transmission part is to be twice as much as that of the color filter corresponding to the reflection part. When the thickness of the color filter on the transmission part is to be 2×L, and the thickness of the color filter on the reflection part is formed to be L, the transmittance feature in  FIG. 3B  can be obtained in both transmission and reflection modes and the same color purity can be represented. 
     Thus, the present invention suggests a method for obtaining same color purity and same transmittance both on the reflection mode and the transmission mode by forming the color filter having different thickness on the color filter substrate to control the cell gaps of the reflection part and of the transmission part. 
       FIG. 4  is a partial cross sectional view of an exemplary transflective liquid crystal display device according to the present invention. In  FIG. 4 , the switching device is omitted for convenience. In  FIG. 4 , a color filter  107  having a step may be formed on a transparent substrate  105  of a color filter substrate  110 . Specifically, a color filter  107   b  corresponding to a reflection part may protrude into a liquid crystal material layer  130  region more than a color filter  107   a  corresponding to the transmission part. In addition, a coating layer  140  and a transparent electrode  145  may be formed on the color filters  107   a  and  107   b.    
     An exemplary method of fabricating the color filter of  FIG. 4  may include forming a black matrix pattern  128  on a transparent substrate  115 , then forming red, green, and blue patterns for realizing colors during a pigment dispersion method. The pigment dispersion method uses a negative photoresist (PR), wherein during a development process a developer may remove the non-exposed portion. The development process may include a dipping, a puddle, or a shower spray method, and the color filter patterns may be fixed by performing a post-bake process. 
       FIGS. 5A through 5C  are cross sectional views of an exemplary fabrication process for color filters according to the present invention. In  FIGS. 5A  to  5 C, the fabrication process of a red color sub-pixel will be described as an example. In  FIG. 5A , a black matrix  106  pattern may be formed on a transparent substrate  105 , then the color filter  107   a  corresponding to the transmission part of the red color sub-pixel pattern may be formed. Next, the green and blue color sub-pixel patterns of the transmission part may be formed by shift exposing a mask (not shown) after changing the pigment repeatedly. Next, the red color sub-pixel pattern may be fixed by a post-bake process. 
     In addition, a transparent material  108  may be formed on the black matrix  106  and the transparent substrate  105  at opposing side portions of the color filter  107   a  at a predetermined thickness using the mask (in FIG.  5 B). The thickness of the transparent material  108  may be controlled to make the cell gap of the transmission part twice as thick as that of the reflection part. The transparent material  108  may includes an organic resin or an acrylic resin. 
     In  FIG. 5C , the color filter  107   b  corresponding to the reflection part of the red color sub-pixel pattern may be formed and patterned by selectively etching the color pigment after applying the color pigment on portions of the transparent material  108 . The patterned color filter  107   b  may be fixed by performing the post-bake process. Then, the mask may be shifted to form the green and blue color sub-pixel patterns of the reflection part. Accordingly, a thickness of the color filter  107   a  on the transmission part may be made to be twice as thick as that of the color filter  107   b  on the reflection part. Thus, the transmittance of light may be the same in both the reflection mode and the transmission mode. If pigments having different transmittances are used for the reflection part and for the transmission part, the thickness of the cell gap and of the color filter may be more flexibly controlled. 
     Another method for forming the color filter may be to print red, green, and blue color inks on the substrate using various other printing methods. The printing methods may include screen-printing, offset printing, and graphic printing methods. Therefore, the color filter may be sequentially formed in  FIG. 5  using the printing methods. 
     After forming a coating layer  140  on the color filter substrate upon which the red, green, and blue color sub-pixel patterns may be formed, a transparent electrode  145 , such as an indium tin oxide (ITO), may be deposited on entire surface of the color filter substrate  110  to functions as a common electrode for driving the liquid crystal cell (in FIG.  4 ). In addition, a gate insulating layer  122 , a passivation layer  126 , a pixel electrode  127 , and a reflection electrode  128  may be formed on an array substrate facing the completed color filter substrate  110 . A part of the reflection electrode  128  facing toward the color filter  107   a  of the transmission part on the color filter substrate  110  may be removed in order to form the transmission part in the pixel region. Then, a liquid crystal material layer  130  may be formed between the color filter substrate  110  and the array substrate  120 . However, this fabrication process may be problematic in that an addition mask process for forming the color filters on the transmission part and on the reflection part are fabricated separately. 
       FIG. 6  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention. The exemplary embodiment may have a same structure as that of the liquid crystal display device of the  FIGS. 4 and 5A  to  5 C, except for the structure of the color filter portion on the color filter substrate. Thus, descriptions for the same components as those of the liquid crystal display device in  FIGS. 4 and 5  to  5 C are omitted, and new components of the exemplary embodiment will be described. Hereinafter, same reference numerals are used for the same components as those of FIG.  4 . 
     In  FIG. 6 , after etching a part of a transparent substrate  205  corresponding to the transmission part to be a predetermined thickness in order to construct the transmission part, a color filter  207   a  may be formed on the etched portion by applying the color pigment onto the entire substrate and by selectively patterning. Then, the color pigment may be applied again and the part corresponding to the reflection part may be selectively patterned to form the color filter  207   b  corresponding to the reflection part on both sides of the transmission part. The color filters  207   a  and  207   b  may be formed by the pigment dispersion method or by the printing method. 
     The thickness of the color filter  207   a  on the transmission part may be determined by a degree of etching of the substrate, and the thickness of the color filter  207   b  on the reflection part may also be determined. The cell gap of the transmission part may be made to be twice as thick as that of the reflection part using the step generated on the above two portions. If the step is formed on the color filter substrate in order to make the cell gap of the transmission part thicker than that of the reflection part as in the embodiments of  FIGS. 4 and 5A  to  5 C and  FIG. 6 , then distortion of an electric field may be generated due to the step of the electrodes when the voltage is applied to the liquid crystal display device. Thus, the aligning direction of the liquid crystal material may not be uniform on the stepped portion and light leakage may be generated. The light leakage may function as an element interrupting a contrast on the screen, and therefore, it may be desirable that the step of the color filters generated on the boundary of transmission part and reflection part may be small. In order to make the step smaller, the following method is described. 
       FIG. 7  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention. In  FIG. 7 , a thickness of a transparent material  308  may be reduced and a passivation layer  326  of an array substrate  120  may be etched as much as the reduced thickness to form cell gaps of reflection and transmission parts. The passivation layer  326  corresponding to the transmission part of the array substrate  120  may be etched some or whole so that the cell gap of the transmission part is twice as thick as that of the reflection part. 
     Therefore, the step of the color filter substrate caused by the difference of thickness between the color filter  307   a  on the transmission part and the color filter  307   b  on the reflection part of the color filter substrate  110  may be reduced, and therefore, the light leakage generated on the stepped portion can be reduced. 
       FIG. 8  is a partial cross sectional view of another exemplary transflective liquid crystal display device according to the present invention. In  FIG. 8 , an etched thickness of a transparent substrate  405  on a color filter substrate  110  may be reduced from a fabrication method of the embodiment of  FIG. 6 , and a passivation layer  426  of the array substrate  120  may be etched as much as the reduced thickness to form the cell gap of the transmission part. The passivation layer  426  corresponding to the transmission part of the array substrate  120  may be etched some or whole so that the cell gap of the transmission part is twice as thick as that of the reflection part. 
     Therefore, the step of the color filter substrate  110  caused by the difference of the thickness between the color filter  407   a  on the transmission part and the color filter  407   b  on the reflection part of the color filter substrate  110 , and therefore, the light leakage generated on the stepped portion can be prevented. 
     The steps formed on the reflection part and the transmission part of the color filter substrate in the embodiments of  FIGS. 7 and 8  may be reduced less than those of the embodiments of  FIGS. 4 and 6 . When the step may be formed on the array substrate, inferiority may be generated easily during the fabrication process since the step is large. However, when the step may be also formed on the color filter substrate as in the above embodiments, the inferiority can be reduced less than that of the above case during the process since the step on the array substrate is reduced. 
     Also, the surface of the substrate may be flattened, and therefore, the image property may be improved, and the light leakage due to the step on the electrode can be prevented. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the transflective liquid crystal display device and the method of fabricating the same of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present inventions cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.