Abstract:
A liquid crystal display device includes first and second substrates facing and spaced apart from each other, a liquid crystal layer interposed between the first and second substrates, a transparent common electrode disposed on the first substrate, a gate line disposed on the second substrate along a first direction, a data line disposed on the second substrate along a second direction perpendicular to the first direction, a thin film transistor disposed at an intersection of the gate line and the data line, a gate insulation layer disposed on the second substrate, a passivation layer disposed on the gate insulation layer, and a reflective electrode disposed on the passivation layer, wherein the reflective electrode overlaps end portions of the data line.

Description:
This application claims the benefit of Korean Patent Application No. 2000-48236, filed on Aug. 21, 2000, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (LCD) device, and more particularly, to reflective and transflective LCD devices having black resin. 
     2. Description of Related Art 
     Until now, the cathode-ray tube (CRT) has been developed and mainly used for display systems. However, flat panel displays are beginning to make an appearance because of their small depth dimensions, desirably low weight, and low voltage power supply requirements. Presently, thin film transistor-liquid crystal displays (TFT-LCDs) with high resolution and small depth dimension are being developed. 
     During operation of the TFT-LCD, a pixel is turned ON by switching elements to transmit light generated from a backlight device. The switching elements are generally amorphous silicon thin film transistors (a-Si:H TFTs) that use an amorphous silicon layer. Advantageously, the amorphous silicon TFTs can be formed on low cost glass substrates using low temperature processing techniques. 
     In general, the TFT-LCD transmits image data using light emitted from the backlight device that is positioned under a TFT-LCD panel. However, the TFT-LCD only employs 3˜8% of the incident light generated from the backlight device, thereby providing inefficient optical modulation. In the TFT-LCD device, two polarizers will typically have a transmittance of 45% and two corresponding substrates will typically have a transmittance of 94%. The TFT array and the pixel electrode may have a transmittance of 65% and the color filter may have a transmittance of 27%. Therefore, the typical transmissive TFT-LCD device has a relative transmittance of about 7.4% as shown in FIG.  1 . Additionally, FIG. 1 also shows the relative transmittance after light passes through each layer of the device. For this reason, the transmissive TFT-LCD device requires a light source having a relatively high initial brightness. However, such a high initial brightness increases electric power consumption requirements of the backlight device. Accordingly, a relatively heavy battery is needed to supply sufficient power to the backlight device. Moreover, use of the battery source will limit the time in which the TFT-LCD can properly operate. 
     In order to overcome these problems, a reflective TFT-LCD has been developed. Since the reflective TFT-LCD device uses ambient light as a light source, the device is light and portable. Additionally, the reflective TFT-LCD device has a superior aperture ratio as compared to a transmissive TFT-LCD device. Namely, since the reflective TFT-LCD substitutes an opaque reflective electrode for a transparent electrode material in the pixel of the conventional transmissive TFT-LCD, the opaque reflective electrode reflects ambient light. Accordingly, since the reflective TFT-LCD device uses ambient light rather than an internal light source, battery life of the reflective TFT-LCD can be increased resulting in a longer period of use. In other words, the reflective TFT-LCD device is driven using light reflected from the reflective electrode, thereby only drive circuitry that drives the liquid crystal uses the battery source in the reflective TFT-LCD device. 
     FIG. 2 is a schematic cross-sectional view of a conventional reflective liquid crystal display device. In FIG. 2, the reflective LCD device  20  comprises an upper substrate  2 , a lower substrate  4 , and a liquid crystal layer  3  interposed therebetween. On a first surface of the upper substrate  2  that opposes the lower substrate  4 , a black matrix  6  isolates color filters  8  (Red, Green and Blue) that are disposed on the first surface of the upper substrate  2 . The color filters  8  and the black matrix  6  are disposed on a similar plane, and a transparent common electrode  10  is disposed on the color filters  8  and black matrix  6 . 
     A gate insulation layer  18  is disposed on a first surface of the lower substrate  4  that opposes the first surface of the upper substrate  2 . A passivation layer  14  is disposed on the gate insulation layer  18 , and data lines  16  that transmit data signals to the TFT (not shown) are disposed between the gate insulation layer  18  and the passivation layer  14  and on both sides of a pixel region. A reflective electrode  12  is disposed on the passivation layer  14  and, in combination with the transparent electrode  10 , controls orientation of liquid crystal molecules  9  by application of an electric field. The reflective electrode  12  reflects ambient light to display image data and functions as a pixel electrode. Furthermore, since the reflective LCD device  20  displays image data using the ambient light, lateral side edges of the reflective electrode  12  overlap portions of the data lines  16 , thereby increasing aperture ratio. The reflective electrode  12  is formed of an opaque metallic material that has superior light reflectance, while the passivation layer  14  is formed of an insulating material that has a low dielectric constant of about 3 (ε≈3), such as benzocyclobutene (BCB) or acryl-based resin, for example. Accordingly, since the passivation layer is disposed between the reflective electrode  12  and the data lines  16 , electrical interference, i.e., cross talk, is prevented. Here, a thickness of the passivation layer  14  is about 1.5 micrometers (μm). 
     In FIG. 2, an overlap area “A” represents an area of the pixel electrode  12  that overlaps the data line  16 . Since the data line  16  is shielded from incident light by this overlap area “A” of the pixel electrode  12 , a substantial portion of the black matrix  6  corresponding to the overlap area “A” can be removed. However, if the portion of the black matrix  6  corresponding to the overlap area “A” is removed, a width of the black matrix  6  is narrowed, thereby creating misalignment problems during manufacturing processes. For example, the misalignment of the red, green and blue color filters  8  is created due to a small aligning margin of the black matrix  6 , and the misalignment of the upper and lower substrates is created when attaching the upper substrate  2  to the lower substrate  4 . The width of the overlap area “A” is about 2 μm, and a width of the black matrix is ideally about 4 μm. However, in practice the ideal width of the black matrix is difficult to obtain because of the above-mentioned problems. Accordingly, a width of more than 4 μm needs to be maintained for the black matrix so that the overlap area “A” is covered by the black matrix. Thus, increasing the aperture ratio is difficult. 
     Meanwhile, the reflective TFT-LCD device can be adversely affected by its surroundings. For example, the brightness of indoor ambient light differs greatly from the brightness of outdoor ambient light. In addition, the brightness of the outdoor ambient light is dependent upon the time of day (i.e., noon or dusk) such that the reflective TFT-LCD device cannot be used at night without sufficient ambient light. Accordingly, there is a need for a transflective TFT-LCD device that can be used during daylight hours, as well as nighttime, since the transflective LCD device can be changed to either a transmissive mode or a reflective mode depending on the desired condition of operation. 
     FIG. 3 is a schematic cross-sectional view of a pixel area of a conventional transflective liquid crystal display device. In FIG. 3, the transflective TFT-LCD device includes a liquid crystal panel  45  and a backlight device  44 . The liquid crystal display panel  45  includes an upper substrate  22 , a lower substrate  24  and a liquid crystal layer  31  interposed therebetween. The upper substrate  22  and the lower substrate  24  are commonly referred to as a color filter substrate and an array substrate, respectively. The upper substrate  22  includes a black matrix  26  and color filters  28  on a surface of the upper substrate  22  that faces the lower substrate  24 , and a transparent common electrode  30  is formed on the color filters  28  and black matrix  26 . Here, the black matrix  26  and color filters  28  are located in a common plane. 
     In FIG. 3, the lower substrate  24  has a gate insulation layer  33  disposed on a surface that faces the upper substrate  22  and data lines  34  are formed on the gate insulation layer  33 . A passivation layer  32  is formed on the gate insulation layer  33  while covering the data lines  34  and has a trapezoidal-shaped transmitting hole  42 . Thus, the passivation layer  32  has inclined portions disposed adjacent to the transmitting hole  42 . A transparent electrode  36  is formed on the passivation layer  32  and is disposed within the transmitting hole  42 , and an interlayer insulator  38  and a reflective electrode  40  are formed in series on the transparent electrode  36 . The interlayer insulator  38  electrically insulates the reflective electrode  40  from the transparent electrode  36 . 
     In the transflective liquid crystal display device described above, the reflective electrode  40  and the transparent electrode  36  function together as a pixel electrode. Furthermore, the lower substrate  24  is divided into a reflective portion “r” and a transmitting portion “t” such that the passivation layer  32  is formed to create different cell gaps between the reflective portion “r” and the transmitting portion “t.” Namely, a first cell gap is defined by an interval, i.e., the reflective portion, between the reflective electrode  40  and the transparent common electrode  30 , and a second cell gap is defined by an interval, i.e., the transparent portion, between the transparent electrode  36  and the transparent common electrode  30 . As shown in FIG. 3, the passivation layer  32  of the array substrate  24  is formed to create a step difference between the first cell gap and the second cell gap. Thus, the thickness of the liquid crystal layer  31  is different within each of the first and second cell gaps. Preferably, the second cell gap is twice as long as the first cell gap. 
     As previously described, the reflective electrode  40  in the reflective portion “r” reflects the ambient light, while the transparent electrode  36  in the transmitting portion “t” transmits the light emitted from the backlight device  44 . In this structure, the reflective electrode  40  overlaps a portion of the data line  34 , thereby forming an overlap area “E.” The overlap area “E” extends the pixel region and the aperture ratio similar to the reflective LCD device shown in FIG.  2 . However, it is difficult to obtain a desired aperture ratio because a width of the black matrix  26  is required to be about 4 μm. Moreover, as previously described, if a portion of the black matrix  26  corresponding to the overlap area “E” is removed, the width of the black matrix  26  is narrowed, thereby creating misalignment problems during manufacturing processes. For example, the misalignment of the red, green and blue color filters  28  occurs due to a small alignment margin of the black matrix  26 , and the misalignment of the upper and lower substrates occurs when attaching the upper substrate  22  to the lower substrate  24 . 
     Furthermore, in the transflective LCD device shown in FIG. 3, portions of the reflective electrode  40  are positioned on the inclined portions of the interlayer insulator  38  to prevent light leakage. In addition, extended portions “F” of the reflective electrode  40  are disposed along a peripheral planar portion of the interlayer insulator  38  disposed within the transmitting hole  42 . The extended portions “F” decrease a margin of the light leakage error. Therefore, the aperture ratio decreases because the extended portions “F” of the reflective electrode  40  cover a peripheral portion of the transmitting hole  42  in a transmissive mode of the transflective LCD device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to reflective and transflective liquid crystal display devices having black resin 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 reflective and transflective liquid crystal display devices with increased aperture ratios. 
     Another object of the present invention is to provide reflective and transflective liquid crystal display devices with improved manufacturing processes. 
     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, the liquid crystal display device includes first and second substrates facing and spaced apart from each other, a liquid crystal layer interposed between the first and second substrates, a transparent common electrode disposed on the first substrate, a gate line disposed on the second substrate along a first direction, a data line disposed on the second substrate along a second direction perpendicular to the first direction, a thin film transistor disposed at an intersection of the gate line and the data line, a gate insulation layer disposed on the second substrate, a black resin layer disposed on the gate insulation layer, and a reflective electrode disposed on the passivation layer, wherein the reflective electrode overlaps end portions of the data line. 
     In another aspect, the liquid crystal display device includes first and second substrates facing and spaced apart from each other, a liquid crystal layer interposed between the first and second substrates, a backlight device disposed adjacent to the second substrate for generating light, a transparent common electrode disposed on the first substrate, a gate line disposed on the second substrate along a first direction, a data line disposed on the second substrate along a second direction perpendicular to the first direction, a thin film transistor disposed at a crossing of the gate line and the data line, a gate insulation layer disposed on the second substrate, a passivation layer disposed on the gate insulation layer, the passivation layer having a transmitting hole extending to the gate insulation layer, and the passivation layer made of a black resin, a transparent electrode having a first portion disposed on the passivation layer and a second portion disposed within the transmitting hole, and a reflective electrode formed on the passivation layer, wherein the reflective electrode overlaps end portions of the data line. 
     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 graph illustrating a relative transmittance measured after light passes through each layer of a conventional liquid crystal display (LCD) device; 
     FIG. 2 is a schematic cross-sectional view of a conventional reflective liquid crystal display device; 
     FIG. 3 is a schematic cross-sectional view of a pixel area of a conventional transflective liquid crystal display device; 
     FIG. 4 is a schematic plan view of one pixel of an exemplary reflective liquid crystal display device according to the present invention; 
     FIG. 5 is a schematic cross-sectional view taken along line V—V of FIG. 4; 
     FIG. 6 is a schematic plan view of one pixel of another exemplary transflective liquid crystal display device according to the present invention; and 
     FIG. 7 is a schematic cross-sectional view taken along line VII—VII of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts. 
     FIG. 4 is a schematic plan view of one pixel of an exemplary reflective liquid crystal display device according to the present invention. In FIG. 4, a gate line  102  is arranged in a transverse direction, while a data line  106  is arrzanged in a longitudinal direction. At a crossover point of the gate line  102  and the data line  106 , a thin film transistor (TFT) “T” is disposed. The TFT “T” may include a gate electrode  104 , a source electrode  108  and a drain electrode  110 . The gate electrode  104  may extend from the gate line  102 , and the source electrode  108  may extend from the data line  106  and overlap a portion of the gate electrode  104 . The drain electrode  110  is spaced apart from the source electrode  108  and overlaps another portion of the gate electrode  104 . A reflective electrode  114  may be formed in a pixel region defined by a pair of gate lines  102  and data lines  106 . A portion of the reflective electrode  114  overlaps a portion of the drain electrode  110  and is electrically connected to the drain electrode  110 . Lateral side portions of the reflective electrode  114  may overlap corresponding portions of the data lines  106  in an overlap area “B” (see FIG. 5, for example), thereby increasing a pixel area and an aperture ratio. The reflective electrode  114  may include metallic materials, such as aluminum (Al) or Al-alloy, having superior reflectivity. 
     FIG. 5 is a schematic cross-sectional view taken along line V—V of FIG.  4 . In FIG. 5, the inventive liquid crystal display device  150  includes an upper substrate  120 , a lower substrate  100  and a liquid crystal layer  130  disposed therebetween. In contrast to the conventional reflective liquid crystal display device shown in FIG. 2, a first surface of the upper substrate  120  that opposes a first surface of the lower substrate  100  includes a color filter layer  122  without a black matrix. A transparent common electrode  124  is formed on the color filter layer  122  and may include a transparent material such as indium tin oxide and indium zinc oxide, for example. 
     In FIG. 5, a gate insulation layer  105  is disposed on the first surface of the lower substrate  100  and a passivation layer  112  is disposed on the gate insulation layer  105 . Furthermore, data lines  106  that transmit data signals to the TFT (in FIG. 4) are disposed between the gate insulation layer  105  and the passivation layer  112  and are also disposed on opposing sides of a pixel region. A reflective electrode  114  is disposed on the passivation layer  112  and together with the transparent common electrode  124  controls liquid crystal molecules of the liquid crystal layer  130  by application of an electric field, thereby reflecting ambient light to display image data. 
     In the exemplary reflective LCD device of FIG. 5, the reflective electrode  114  may also function as a pixel electrode with lateral side portions of the reflective electrode  114  overlapping corresponding portions of the data lines  106  at overlap areas “B,” thereby increasing an aperture ratio. Thus, overlap areas “B” may be created at opposing lateral side portions of the reflective electrode  114 . The passivation layer  112  may be made of black resin to function not only as an insulator but also as a light shielding layer. Accordingly, the passivation layer  112  prevents the transparent common electrode  124  from being exposed to incident light in an outside area of the reflective electrode  114  in the pixel region. In contrast to the conventional art, since the passivation layer  112  is formed of the black resin, a black matrix is not required on a surface of the upper substrate  120 , thereby simplifying the manufacturing processes. 
     Furthermore, the overlap area “B” represents an area of the pixel electrode  114  that overlaps the data line  106 . Compared to the conventional reflective LCD device, since the black matrix is not formed on the upper substrate  120 , a margin of the overlap area “B” between the reflective electrode  114  and the date line  106  can be maximized, thereby achieving a high aperture ratio. 
     FIG. 6 is a schematic plan view of one pixel of another exemplary transflective liquid crystal display device according to the present invention. In FIG. 6, a gate line  204  is arranged in a transverse direction, while a data line  210  is arranged in a longitudinal direction. At a crossover point of the gate line  204  and the data line  210 , a thin film transistor (TFT) “T” is disposed. The TFT “T” may include a gate electrode  206 , a source electrode  212  and a drain electrode  214 . The gate electrode  206  may extend from the gate line  204 , and the source electrode  212  may extend from the data line  210  and overlap a portion of the gate electrode  206 . The drain electrode  214  is spaced apart from the source electrode  212  and overlaps another portion of the gate electrode  206 . 
     In FIG. 6, a transparent electrode  218  and a reflective electrode  222 , which together function as a pixel electrode, are formed in a pixel region defined by a pair of gate lines  204  and data lines  210 . The transparent electrode  218  is electrically connected with the drain electrode  214  through a drain contact hole. Lateral side portions of the reflective electrode  222  may overlap corresponding portions of the data lines  210  in an overlap area “C” (see FIG. 7) formed at both lateral side portions of the reflective electrode  222 , thereby increasing a pixel area and an aperture ratio. The transparent electrode  218  may include transparent materials such as indium tin oxide and indium zinc oxide, for example. The reflective electrode  222  may include metallic materials, such as aluminum (Al) or Al-alloy, having superior reflectivity. The reflective electrode  222  may include a transmitting hole ( 224  also shown in FIG. 7) disposed in a central portion of the reflective electrode  222 . Accordingly, the reflective electrode  222  reflects ambient light to display image data in the reflective mode, and the transmitting hole  224  transmits artificial light generated from a backlight device (see reference element  240  of FIG. 7) to display image data in a transmissive mode. 
     FIG. 7 is a schematic cross-sectional view taken along line VII—VII of FIG.  6 . In FIG. 7, the transflective TFT-LCD device may include a liquid crystal panel  200  and a backlight device  240 . The liquid crystal display panel  200  includes an upper substrate  230 , a lower substrate  202  and a liquid crystal layer  228  disposed therebetween. The upper substrate  230  and the lower substrate  202  are referred to as a color filter substrate and an array substrate, respectively. The upper substrate  230  may include a color filter layer  226  disposed on a first surface that faces the lower substrate  202  and a transparent common electrode  232  may be disposed on the color filter layer  226 . The transparent common electrode  232  may include a transparent material such as indium tin oxide and indium zinc oxide, for example. 
     Furthermore, the lower substrate  202  may include a gate insulation layer  208  disposed on a first surface of the lower substrate that faces the upper substrate  230 . Data lines  210  may be formed on the gate insulation layer  208 , and a passivation layer  216  may be formed on the gate insulation layer  208  to cover the data lines  210 . The passivation layer  216  may include a transmitting hole  224 . The transmitting hole  224  may include a polygonal shape such as a trapezoid, for example. Accordingly, the passivation layer  216  may have inclined portions disposed laterally about the transmitting hole  224 . A transparent electrode  218  may be disposed on the passivation layer  216  and include portions disposed within the transmitting hole  224 . The transparent electrode  218  may include a transparent material including indium tin oxide and indium zinc oxide, for example. Further, an interlayer insulator  220  may be disposed on the transparent electrode  218  and may have portions disposed on the passivation layer  216  so as to laterally surround end portions of the transparent electrode  218 . A reflective electrode  222  that may include a transmitting hole  224  may be disposed on the interlayer insulator  220 . The interlayer insulator  220  electrically insulates the reflective electrode  222  from the transparent electrode  218 . 
     Although FIG. 7 specifically shows the reflective electrode  222  disposed above the transparent electrode  218 , the transparent electrode  218  can be disposed over the reflective electrode  222 . In other words, the transparent electrode  218  may be interchanged with the reflective electrode  222 . In this instance, the interlayer insulator  220  may be formed between the reflective electrode  222  and the transparent electrode  218 . 
     In the present exemplary transflective liquid crystal display device described above, the reflective electrode  222  and transparent electrode  218  together may function as a pixel electrode. Further, the lower substrate  202  may be divided into a reflective portion “R” and a transmitting portion “T.” As previously described, the passivation layer  216  may be disposed to create different cell gaps between the reflective portion “R” and the transmitting portion “T.” The passivation layer  216  may be made of black resin to function not only as an insulator but also as a light shielding layer. Accordingly, the black resin is not required on the upper substrate  230 , thereby simplifying manufacturing processes of the transflective liquid crystal display device. 
     As previously described with respect to FIG. 7, the reflective electrode  222  in the reflective portion “R” reflects the ambient light, while the transparent electrode  218  in the transmitting portion “T” transmits the light emitted from the backlight device  240 . In this structure, the reflective electrode  222  overlaps a lateral end portion of the data line  210 , thereby creating an overlap area “C.” The overlap area “C” extends a pixel region and an aperture ratio similar to the reflective LCD device shown in FIG.  5 . Compared to the conventional transflective LCD device, since the black resin is not formed on the upper substrate  230 , a width of the overlapped area “C” can be maximized, thereby obtaining a high aperture ratio in the reflective mode of the transflective liquid crystal display device. 
     Furthermore, since the black resin is employed as the passivation layer  216 , light leakage does not occur within an inclined area “D.” Therefore, as compared to the conventional device shown in FIG. 3, a portion of the reflective electrode  222  is not required to extend onto the interlayer insulator  220  within the transmitting hole  224  of the transmitting portion “T” to prevent light leakage. Accordingly, the aperture ratio increases in the transmissive mode of the exemplary transflective liquid crystal display device of the present invention. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the reflective and transmissive liquid crystal display devices having black resin of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.