Abstract:
A color filter substrate includes a substrate, a plurality of buffer layers respectively on the substrate, the plurality of buffer layers being spaced apart from adjacent buffer layers with an interval such that they have the shape of a matrix, a plurality of color filter layers on the buffer layers such that the plurality of color filter layers have the shape of matrix, each color filter layer having first and second portions, the first portion disposed in the gap between two adjacent buffer layers while the second portion is disposed on upper surfaces of the two adjacent buffer layers, the plurality of color filter layers being used for the transflective LCD device; and a common electrode on the plurality of color filter layers. In fabricating the color filter layer, the first and second portions of the color filter layer are integrally formed. Therefore, a simple fabricating process is achieved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display (LCD) device implementing a color filter having various thickness.  
           [0003]    2. Discussion of the Related Art  
           [0004]    LCD devices are usually classified into transmission type and reflection type according to their difference in a light source.  
           [0005]    The transmission type LCD device uses light incident from a back light that is attached to a rear surface of a liquid crystal panel. The light is incident to a liquid crystal layer of the liquid crystal panel, and is absorbed or passes through the liquid crystal layer according to proper alignments of the liquid crystal layer. The alignment of the liquid crystal layer can be controlled by way of controlling an electric field, which is applied to the liquid crystal layer. Therefore, a transmittance ratio of the liquid crystal panel can be controlled by way of applying the electric field to the liquid crystal layer. Conventionally, the back light of the transmission type LCD device is an artificial light source. Therefore, high power consumption due to the back light is a greater disadvantage of the transmission type LCD device.  
           [0006]    On the contrary to the above-mentioned transmission type LCD device, the reflection type LCD device uses an ambient light incident from a natural light source or an exterior artificial light source. Because of its low power consumption, the reflection type LCD device is focused on. However, the reflection type LCD device is useless when the whether or exterior light source is dark.  
           [0007]    Accordingly, a transflective LCD device is developed to compensate for the reflective type LCD device. The transflective LCD device is useful regardless of the whether or exterior light source. FIG. 1 is an exploded perspective view illustrating a typical transflective LCD device.  
           [0008]    The transflective LCD device  1  includes upper and lower substrates  10  and  20  that are opposed with each other, and an interposed liquid crystal layer  50  therebetween. The upper and lower substrates  10  and  20  are called a color filter substrate and an array substrate, At respectively. In the upper substrate  10 , on a surface opposing the lower substrate  20 , black matrix  12  and color filter layer  14  that includes a plurality of red (R), green (G), and blue (B) color filters are formed. That is to say, the black matrix  12  surrounds each color filter, in shape of an array matrix. Further on the upper substrate  10 , a common electrode  16  is formed to cover the color filter layer  14  and the black matrix  12 .  
           [0009]    In the lower substrate  20 , on a surface opposing the upper substrate  10 , a TFT “T” as a switching device is formed in shape of an array matrix corresponding to the color filter layer  14 . In addition, a plurality of crossing gate and data lines  26  and  28  are positioned such that each TFT is located near each cross point of the gate and data lines  26  and  28 . Further on the lower substrate  20 , a plurality of reflective electrodes  22  are formed on an area defined by the gate and data lines  26  and  28 . The area there defined is called a pixel region “P.” Each reflective electrode  22  has a transmissive portion  22   a  thereon. The transmissive portion  22   a  beneficially has a shape of a through hole such that it exposes a transparent electrode  24  disposed below the reflective electrode  22 . The reflective electrode  22  is beneficially made of a metal having a high reflectivity, and the transparent electrode  24  is beneficially made of a transparent conductive material, usually indium tin oxide (ITO) or indium zinc oxide (IZO).  
           [0010]    [0010]FIG. 2 shows a cross-sectional view illustrating the transflective LCD device of FIG. 1. As shown, between the upper and lower substrates  10  and  20 , a liquid crystal layer  50  is interposed. The upper substrate  10  has the color filter layer  14  and common electrode  16  on the inner surface opposing the lower substrate  20 . On the common electrode  16 , an upper alignment layer  142  is formed. In addition, on the exterior surface of the upper substrate  10 , a retardation film or a half wave plate (HWP)  46  and an upper polarizer  54  are sequentially disposed. The half wave plate (HWP)  46  serves to involve a phase difference of “λ/2” for incident rays such that the incident rays rotate to have a phase difference of “λ/2” after passing through the half wave plate  46 .  
           [0011]    In the meanwhile, the lower substrate  20  has the reflective electrode  22  and transparent electrode  24  on its surface opposing the upper substrate  10 . A lower alignment layer  44  is formed on the reflective electrode  22  and exposed portion of the transparent electrode  24 . Between the reflective and transparent electrode  22  and  24 , a passivation layer  48  is interposed to separate them. The reflective electrode  22  has the transmissive portion  22   a , which exposes the transparent electrode  24 . In addition, on the exterior surface of the lower substrate  20 , a lower polarizer  52  is disposed, and below the lower polarizer  52 , a back light  40  is disposed.  
           [0012]    For forming the reflective and transparent electrode  22  and  24 , at first, the transparent conductive material selected from indium tin oxide (ITO) or indium zinc oxide (IZO) is deposited on the lower substrate  20 . The transparent conductive layer is patterned to form the transparent electrode  24 . Then, an insulating material is deposited on the transparent electrode  24  to form the passivation layer  48 . On the passivation layer  48 , aluminum (Al) based metal of a high reflectivity is deposited and patterned such that the reflective electrode  22  is formed. At this point, portions of the reflective electrode  22  and passivation layer  48  are sequentially etched away to form the transmissive portion  22   a.    
           [0013]    The liquid crystal layer  50  between the upper and lower substrates  10  and  20  has an optical anisotropy. That is to say, in their first state alignment, long axes of the liquid crystal molecules are aligned parallel to the substrates  10  and  20 . Whereas, with an electric field applied across the liquid crystal layer  50 , the long axes of the molecules are aligned perpendicular to the substrates  10  and  20 . Therefore, the liquid crystal layer  50  serves as a switch for incident rays of light. In the later state alignment, a homeotropic alignment, the rays pass through the liquid crystal layer  50 , without a phase difference.  
           [0014]    The liquid crystal layer  50  has a layer thickness or cell gap. Specifically, the liquid crystal layer  50  has a first cell gap “d1” over the reflective electrode  22  and a second cell gap “d2” over the transparent electrode  24 . At this point, the first and second cell gaps “d1” and “d2” beneficially have a definite relationship. That is to say, the second cell gap d2 is beneficially twice as the first cell gap d1 (d2≈2d1). Over the reflective electrode  22 , the liquid crystal layer  50  involves a phase difference of “λ/4.” The above-mentioned different cell gaps “d1” and “d2” improve en efficiency of incident rays passing through the transmissive portion  22   a.    
           [0015]    More detailed explanation is followed with reference to relationships (1) and (2): 
             d 1Δn=λ/4  (1), 
             d 2=2 d 1  (2) 
           [0016]    , such that d2Δn=λ/2, wherein “d1” is the first cell gap over the reflective electrode  22 , “d2” is the second cell gap over the transmissive portion  22   a  or transparent electrode  24 . The first relationship (1) about the phase difference “λ/4” means that rays get the phase difference of “λ/4” after passing through the liquid crystal layer  50  of the first cell gap “d1” over the reflective electrode  22 . Similarly, the relationship “d2Δn=λ/2” means that the rays get the phase difference of “λ/2” after passing through the liquid crystal layer  50  of the second cell gap “d2” over the transmissive portion  22   a.    
           [0017]    Rays from the back light  40  pass through the lower polarizer  52  and are linearly polarized according to a first transmittance axis of the lower polarizer  52 . That is to say, the lower polarizer  52  transmits only a portion of the incident rays that has a corresponding vibration direction parallel to the first transmittance axis of the lower polarizer  52 . A vibration direction of rays is perpendicular to a travelling direction of the rays.  
           [0018]    Then, the linearly polarized rays pass through the liquid crystal layer  50  over the transmissive portion  22   a  and get the phase difference of “λ/2”, which is explained above. At this point, the liquid crystal molecules are aligned in the first state alignment without an electric field applied thereto. The phase difference “λ/2” makes the rays rotate such that they have a vibration direction perpendicular to the first transmittance axis of the lower polarizer  52 . After passing through the liquid crystal layer  50 , the rays subsequently pass through the half wave plate (HWP)  46  and get the additional phase difference of “λ/2”, which means that the rays rotate to have a different vibration direction parallel to the first transmittance axis of the lower polarizer  52 . At this point, the upper polarizer  54  has a second transmittance axis perpendicular to the first transmittance axis of the lower polarizer  52 . Therefore, the rays passing through the half wave plate  46  are totally absorbed by the upper polarizer  54  such that a dark state for the transmissive portion  22   a  is achieved. Since the upper polarizer  54  absorbs all the rays, the dark state for the transmissive portion  22   a  is surely dark.  
           [0019]    On the contrary, if the second cell gap d2 is equal to the first cell gap d1, rays passing through the liquid crystal layer  50  over the transmissive portion  22   a  get the phase difference of “λ/4” according to the first relationship (1), d1Δn=d2Δn=λ/4. That is to say, the rays are circularly polarized due to the phase difference “λ/4” of the liquid crystal layer  50 . The circularly polarized rays subsequently pass through the half wave plate  46 , and meet the upper polarizer  54 . At this point, the circularly polarized rays include a parallel portion parallel to the second transmittance axis of the upper polarizer  54 . Therefore, the parallel portion of the circularly polarized rays passes through the upper polarizer  54  such that the dark state has a gray level, which means that the dark state cannot be achieved.  
           [0020]    Accordingly, the different cell gaps “d1” and “d2” are beneficially used for the clear dark state. With reference to FIGS. 3A, 3B,  4 A, and  4 B, operation modes for the typical transflective LCD device will be provided in more detail.  
           [0021]    Phase changes of incident rays result from the operation of the upper and lower polarizers  54  and  52 , liquid crystal layer  50 , and half wave plate  46 . Therefore, FIGS. 3A, 3B,  4 A, and  4 B refer to only the above-specified elements. In addition, as previously mentioned, the liquid crystal layer  50  has a homogeneous alignment at its first state alignment, and a homeotropic alignment with an electric field applied across the liquid crystal layer.  
           [0022]    At first, FIG. 3A illustrates a dark state or mode for the transmissive portion  22   a  of FIG. 2. After rays of incident light from the back light  40  (see FIG. 2) pass through the lower polarizer  52 , they are linearly polarized according to the first transmittance axis of the lower polarizer  52 . At this point, the first transmittance axis has a direction of, for example, 45 degrees with respect to the long axis of the substrate  10  or  20  (see FIG. 1). Therefore, the linearly polarized rays passing through the lower polarizer  52  have the same vibration direction of 45 degrees as the first transmittance axis direction.  
           [0023]    The linearly polarized rays subsequently pass through the liquid crystal layer  50  over the transmissive portion  22   a . At this point, the liquid crystal layer  50  over the transmissive portion  22   a  is in the first state alignment with the second cell gap “d2.” Therefore, the liquid crystal layer  50  over the transmissive portion  22   a  involves the phase difference of “λ/2” such that the linearly polarized rays rotate to be perpendicular to the first transmittance axis of the lower polarizer  52 . Then, the half wave plate  46  additionally involves the same phase difference of “λ/2” such that the linearly polarized rays rotate to be parallel to the first transmittance axis of the lower polarizer  52 . Finally, the upper polarizer  54 , which has the second transmittance axis perpendicular to the first transmittance axis, absorbs all of the linearly polarized rays parallel to the first transmittance axis of the lower polarizer  52 . Accordingly, the dark state of the transmissive portion  22   a  is achieved.  
           [0024]    On the contrary with FIG. 3A, FIG. 3B illustrates a white state for the transmissive portion  22   a  of FIG. 2. At this point, the liquid crystal layer  50  has the homeotropic alignment with an electric field applied across the liquid crystal layer  50 . Therefore, the liquid crystal layer  50  involves an optically isotropic property, and no phase difference occurs due to the liquid crystal layer  50 .  
           [0025]    Rays from the back light  40  are linearly polarized after passing through the lower polarizer  52 . Then, the linearly polarized rays pass through the liquid crystal layer  50  without phase change, and meet the half wave plate  46 . The half wave plate  46  involves the phase difference λ/2 such that the linearly polarized rays are parallel to the second transmittance axis of the upper polarizer  54 . The second transmittance axis has a direction of 135 degrees, for example. Therefore, the upper polarizer  54  transmits all the rays such that the white state of the transmissive portion  22   a  is achieved.  
           [0026]    [0026]FIG. 4A illustrates a dark state for the reflective electrode  22  of FIG. 2. At this point, the liquid crystal layer  50  involves the phase difference of “λ/4”, and is aligned in the first state alignment, the homeotropic alignment with the second cell gap “d2.” At first, the upper polarizer  54  linearly polarizes rays of incident light from an external light source such that they have the same vibration direction of 135 degrees as the second transmittance axis of the upper polarizer  54 . Then, the first linearly polarized rays pass through the half wave plate  46 . The half wave plate  46  rotates the vibration direction of the rays such that the first linearly polarized rays have a vibration direction of 45 degrees.  
           [0027]    Subsequently, the rays pass through the liquid crystal layer  50  over the reflective electrode  22  of FIG. 2. The liquid crystal layer  50  circularly polarizes the rays with the phase difference “λ/4” such that the rays change as left-circularly polarized (LCP) rays. Then, the reflective electrode  22  (see FIG. 2) below the liquid crystal layer  50  reflects the LCP rays such that the LCP rays reverses its phase and travelling direction to be right-circularly polarized (RCP) rays.  
           [0028]    Then, the liquid crystal layer  50  involving the phase difference “λ/4” changes the RCP rays to second linearly polarized rays having a vibration direction of 135 degrees, which is parallel to the second transmittance axis of the upper polarizer  54 . The second linearly polarized rays subsequently pass through the half wave plate  46  and rotate to be perpendicular to the second transmittance axis of the upper polarizer  54 . Since the upper polarizer  54  absorbs all the rays, the dark state of the reflective electrode  22  of FIG. 2 is achieved. As shown in FIGS. 3A and 4A, when the liquid crystal layer  50  is in the first state alignment without applied electric field, the conventional transflective LCD device of FIGS. 1 and 2 provides the dark state.  
           [0029]    On the contrary to FIG. 4A, FIG. 4B illustrates a white state for the reflective electrode  22  of FIG. 2. At this point, the liquid crystal layer  50  is in the homeotropic alignment, which involves no phase difference. At first, the upper polarizer  54  linearly polarizes incident rays from an external light source. The first linearly polarized rays passing through the upper polarizer  54  has the same vibration direction of 135 degrees as the second transmittance axis of the upper polarizer  54 . The first linearly polarized rays subsequently pass through the half wave plate  46 . The half wave plate  46  rotates the vibration direction of the rays such that the first linearly polarized rays have a vibration direction of 45 degrees.  
           [0030]    Then the rays pass through the liquid crystal layer  50  without phase difference and meet the reflective electrode  22  of FIG. 2. The reflective electrode  22  of FIG. 2 reflects the rays such the rays turn to have the vibration direction of 135 degrees, which is perpendicular to the second transmittance axis of the upper polarizer  54 . Subsequently, the rays meet the half wave plate  46 . The half wave plate  46  rotates the vibration direction of the rays such that the rays have a vibration direction of 45 degrees again. Therefore, the upper polarizer  54  transmits all the rays such that the white state of the reflective electrode  22  of FIG. 2 is achieved. As shown in FIGS. 3B and 4B, when the liquid crystal layer  50  is in the homeotropic alignment, the conventional transflective LCD device of FIGS. 1 and 2 provides the white state.  
           [0031]    In another aspect, a color property should be considered in designing the transflective LCD device. Conventionally, the reflective electrode  22  of FIG. 5 implements a better color purity property than the transmissive portion  22   a . As shown in FIG. 5, for a transmissive mode of the transflective LCD device  1 , a first incident light “A” from the back light  40  only once passes through the color filter layer  14  having thickness “t1.” However, for a reflective mode, a second incident light “B” from an exterior light source (not shown) twice passes through the color filter layer  14  having the same thickness “t1.” That is to say, in the transmissive mode, the first incident light “A” is only once colored by the color filter layer  14 . Whereas, in the reflective mode, the second incident light “B” is twice colored by the color filter layer  14 . Therefore, regardless of the difference in luminance of the different light sources, the reflective mode of the reflective LCD device implements a better color purity property than the transmissive mode thereof.  
           [0032]    To overcome the above-mentioned problem, a dual color filter layer having different thickness is conventionally adopted for the transflective LCD device. FIG. 6 shows a typical reflective LCD device having the above-mentioned dual color filter layer. As shown, the conventional dual color filter layer  30  has first and second portions  30   a  and  30   b  according to their thickness and location. Between the dual color filter layer  30  and common electrode  16 , a planar layer  90  is interposed. Specifically, the first portion  30   a  is positioned over the transmissive portion  22   a  and has a second thickness “t2” while the second portion  30   b  is positioned over the reflective electrode  22  and has a third thickness “t3.” The second thickness “t2” is beneficially greater than the third thickness “t3” such that an incident light from the back light  40  to the transmissive portion  22   a  takes more color purity in the transmissive mode. Consequently, the color purity property is uniform regardless of the different modes, the transmissive and reflective modes.  
           [0033]    [0033]FIGS. 7A to  7 D illustrate a fabricating process for the above-mentioned dual color filter layer  30 . Generally, a typical color filter layer is formed on an upper substrate of a LCD device and includes red, green, and blue color resins “R”, “G”, and “B.” In addition, the color filter layer usually includes a black matrix (BM) formed between the color resins to shield incident light.  
           [0034]    At first as shown in FIG. 7A, on a transparent insulating substrate or upper substrate  10  (reference upper substrate  10  of FIG. 6), chromium oxide (CrO x ) and chromium (Cr) are sequentially deposited and patterned to form the black matrix  72 . The black matrix  72  has a patterned shape corresponding to the color filter layers, which will be formed subsequently.  
           [0035]    Since light can only be modulated at the area of the reflective electrode and transparent electrode  22  and  24  of FIG. 2, light passing through intervals between the reflective electrode and metal patterns (reference  28  and  26  of FIG. 1) degrade a display quality and should be eliminated. Therefore, the black matrix  72  is formed to cover the intervals. Further, the black matrix  72  shields an active area of a thin film transistor “T” (see FIG. 1) from light, unless electrical properties of the thin film transistor are deteriorated. For forming the black matrix  72 , an assembly margin is considered.  
           [0036]    Then, as shown in FIG. 7B, a red color resin is deposited and patterned on the substrate  10  to form the first red color filter layer  74 . A photolithography process including an exposure step is used for forming the color filter layer. Since the color resin usually has a characteristic of a negative photoresist, non-exposed portions of the color resin are etched away. Then, green and blue color resins are sequentially deposited and patterned on the substrate  10  to respectively form the first green and blue color filter layers  76  and  78 . Each of the first red, green, and blue color filter layer corresponds to one pixel region “P” shown in FIG. 1.  
           [0037]    Thereafter, as shown in FIG. 7C, another red color resin is deposited and patterned on the first red color filter layer  74  such that a second red color filter layer  84  is formed. The photolithography process is also used for the second red color filter layer  84 . At this point, the second red color filter layer  84  beneficially has the same area and location as the transmissive portion  22   a  shown in FIG. 6. Then, another green and blue color resins are sequentially deposited and patterned on the first green and blue color filter layers  76  and  78 , respectively, such that second green and blue color filter layers  86  and  88  are formed.  
           [0038]    Thereafter, as shown in FIG. 7D, a planar layer  90  is formed to cover the first and second color filter layers. The planar layer  90  is beneficially selected from an organic insulating material such as benzocyclobutene (BCB) and acryl resin, or an inorganic insulating material such as silicon dioxide (SiO 2 ) and silicon nitride (SiN x ). The planar layer  90  serves to compensate the stepped shape of the first and second color filter layers such that a leveled surface is provided for the substrate  10 . On the planar layer  90 , a transparent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO) is deposited to form the common electrode  16 .  
           [0039]    As explained above, the conventional fabricating method for the dual color filter layer needs at least six photolithography processes. Too many photolithography processes cause high material cost and low yield to the above-mentioned conventional fabricating method.  
         SUMMARY OF THE INVENTION  
         [0040]    Accordingly, the present invention is directed to a transflective LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0041]    An object of the present invention is to provide a simple method for fabricating a transflective LCD device having a dual color filter layer.  
           [0042]    In order to achieve the above object, in one aspect, the preferred embodiment of the present invention provides a color filter layer substrate used for a transflective LCD device. The color filter layer substrate includes: a substrate; a plurality of buffer layers respectively on the substrate, the plurality of buffer layers being spaced apart from adjacent buffer layers with an interval such that they have a shape of matrix; a plurality of color filter layers on the buffer layers such that the plurality of color filter layers have a shape of matrix, each color filter layer having first and second portions, the first portion disposed in the gap between two adjacent buffer layers while the second portion disposed on upper surfaces of the two adjacent buffer layers, the plurality of color filter layers being used for the transflective LCD device; and a common electrode on the plurality of color filter layers.  
           [0043]    The first portion of the color filter layer is thicker than the second portion thereof such that a thickness ratio between the first and second portions is 1.1 to 2.5.  
           [0044]    The color filter substrate further includes a plurality of black matrices on the substrate wherein each black matrix is spaced apart from adjacent black matrices.  
           [0045]    The color filter layer substrate of claim 1, wherein the plurality of color filter layer includes red, green, and blue color resins.  
           [0046]    The common electrode is selected from a group consisting of indium tin oxide (ITO) and indium zinc oxide (IZO).  
           [0047]    In another aspect, the present invention provides a method for fabricating a color filter layer substrate. The method includes: forming a buffer layer on the substrate, the buffer layer having a plurality of through holes in shape of the array matrix; forming a plurality of color filter layers on the buffer layer, each color filter layer having first and second portions such that a through hole of the buffer layer receiving the first portion; and forming a common electrode on the plurality of color filter layers.  
           [0048]    The method further includes a step of forming a black matrix on a substrate wherein the black matrix having an array matrix shape.  
           [0049]    In another aspect the present invention provides a transflective liquid crystal display device, which includes: upper and lower substrates opposing each other; liquid crystal layer interposed between the upper and lower substrates; a transparent electrode on the lower substrate; a reflective electrode over the transparent electrode, the reflective electrode having a first through hole, the first through hole exposing the transparent electrode such that the liquid crystal layer facing both the transparent and reflective electrodes; a passivation layer between the reflective and transparent electrode, the first through hole of the reflective electrode passing through the passivation layer; a color filter layer between the upper substrate and liquid crystal layer, the color filter layer having first and second portions, the first portion corresponding to the first through hole of the reflective electrode; a buffer layer between the color filter layer and the upper substrate, the buffer layer having a second through hole, the through hole receiving the first portion of the color filter layer; upper and lower polarizers respectively on exterior surfaces of the upper and lower substrates; a retardation layer between the upper polarizer and upper substrate; and a back light under the lower polarizer.  
           [0050]    The device further includes upper and lower alignment layers, the upper and lower alignment layers directly facing, respectively, upper and lower surfaces of the liquid crystal layer.  
           [0051]    The first portion of the color filter layer is thicker than the second portion thereof such that a thickness ratio between the first and second portions is 1.1 to 2.5.  
           [0052]    In the device, a first cell gap “d1” is measured between the reflective and common electrodes, a second cell gap “d2” is measured between the transparent and common electrodes, and a cell gap ratio “d2/d1” is 1.1 to 2.5.  
           [0053]    The retardation layer is a half wave plate involving a phase difference of “λ/2”, or the retardation layer is a quarter wave plate.  
           [0054]    Another retardation layer is interposed between the lower substrate and lower polarizer.  
           [0055]    The device further includes a black matrix surrounded by the buffer layer.  
           [0056]    The passivation layer is transparent and insulating. The buffer layer is transparent and insulating.  
           [0057]    The lower substrate includes a gate line, a data line, and thin film transistor.  
           [0058]    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 DRAWING  
       [0059]    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.  
         [0060]    In the drawings:  
         [0061]    [0061]FIG. 1 is an exploded perspective view illustrating a typical transflective LCD device;  
         [0062]    [0062]FIG. 2 is a cross-sectional view of the transflective LCD device shown in FIG. 1;  
         [0063]    [0063]FIGS. 3A and 3B are flow diagrams illustrating a transmissive mode for the transflective LCD device;  
         [0064]    [0064]FIGS. 4A and 4B are flow diagrams illustrating a reflective mode for the transflective LCD device;  
         [0065]    [0065]FIG. 5 is the same cross-sectional view as FIG. 2 and illustrates different passages for incident rays from a back light and an exterior light source;  
         [0066]    [0066]FIG. 6 is a cross-sectional view illustrating a transflective LCD device having a dual color filter layer according to the prior art;  
         [0067]    [0067]FIGS. 7A to  7 D are sequential cross-sectional views illustrating a fabricating process for the conventional dual color filter layer;  
         [0068]    [0068]FIG. 8 is a cross-sectional view illustrating a transflective LCD device having a dual color filter layer according to a preferred embodiment of the present invention;  
         [0069]    [0069]FIGS. 9A to  9 F are sequential cross-sectional views illustrating a fabricating process for the inventive dual color filter layer; and  
         [0070]    [0070]FIG. 10 is a partially expanded view of FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0071]    Reference will now be made in detail to the preferred embodiments of the present invention, which are illustrated in the accompanying drawings.  
         [0072]    [0072]FIG. 8 is a cross-sectional view illustrating an LCD device according to the preferred embodiment of the present invention. As shown, between the upper and lower substrates  110  and  120 , a liquid crystal layer  150  is interposed. The upper substrate  110  has the color filter layer  130  and common electrode  116 , which are sequentially formed on the surface opposing the lower substrate  120 . On a surface of the common electrode  116 , an upper alignment layer  142  is formed to face the liquid crystal layer  150 . Between the upper substrate  110  and the color filter layer  130 , a buffer layer  190  is interposed. In addition, on the exterior surface of the upper substrate  110 , a retardation film  146  and an upper polarizer  154  are sequentially disposed. Though a half wave plate (HWP) is used as the retardation layer  146  for the preferred embodiment, a quarter wave plate (QWP) may be used instead of the HWP. The half wave plate (HVWP)  46  preferably involves a phase difference of “λ/2.” The phase difference is usually expressed as a product “dΔn”, where “d” is a cell gap of a liquid crystal layer, and “Δn” is an anisotropy of refraction index for the liquid crystal.  
         [0073]    In the meanwhile, the lower substrate  120  has the reflective electrode  122  and transparent electrode  124  on its surface opposing the upper substrate  110 . Between the reflective and transparent electrode  122  and  124 , a passivation layer  148  is interposed to separate them. The reflective electrode  122  has the transmissive portion  122   a , which exposes the transparent electrode  124 . Preferably, the transmissive portion  122   a  is a through hole communicating with the passivation layer  148 , and the passivation layer  148  has the same sized through hole such that the transmissive portion  122   a  exposes the transparent electrode  124 . In addition, on the exterior surface of the lower substrate  120 , a lower polarizer  152  is disposed, and below the lower polarizer  152 , a back light  140  is disposed. A lower alignment layer  144  corresponding to the upper alignment layer  142  is formed on the reflective electrode  122  and exposed portion of the transparent electrode  124 . Though not shown in FIG. 8, a gate line, a data line, and a thin film transistor (reference  26 ,  28 , and “T” of FIG. 1) are formed in peripheries of the transparent and reflective electrodes  124  and  122 . In addition, another retardation layer (not shown) may be disposed between the lower substrate  120  and lower polarizer  152 .  
         [0074]    The liquid crystal layer  150  has a layer thickness or cell gap. Specifically, a first liquid crystal portion  150   b  has a first cell gap “d1” over the reflective electrode  122 , and a second liquid crystal portion  150   b  has a second cell gap “d2” over the transparent electrode  124 . The first and second cell gaps “d1” and “d2” preferably have a relationship therebetween. That is to say, the second cell gap d2 is about twice as the first cell gap d1 (d2≈2d1). Preferably, a cell gap ratio of “d1/d2” is 1.5 to 2.5. A thickness of the passivation layer  148  is preferably controlled to achieve the above-mentioned relationship between the first and second cell gaps “d1” and “d2.” 
         [0075]    The color filter layer  130  as a dual color filter layer has first and second portions  130   a  and  130   b . The color filter layer  130  has a first thickness “t1”, while the second portion  130   b  has a second thickness “t2.” That is to say, the color filter layer  130  has a stepped portion, the first portion  130   a , which is protruded from the second portion  130   b . The first portion  130   a  corresponds to the transmissive portion  122   a  of the reflective electrode  122  such that the transmissive portion  122   a  involves the same color purity as the reflective electrode  122 . The buffer layer  190  is interposed between the color filter layer  130  and the upper substrate  110  such that a desired thickness ratio “t1/t2” is achieved.  
         [0076]    Several factors should be considered for fabricating the above-mentioned dual-color filter layer  130 . For example, a difference in light sources used for the transparent electrode  124  and reflective electrode  122 , and amount of dye included in the color filter layer  130 . Considering the above-mentioned factors, the color filter layer  130  is designed to have a thickness ratio “t1/t2”, which is over 1.0. Preferably, the thickness ratio “t1/t2” is 1.1 to 2.5 inclusive, and it may vary according to position and color of the color filter layer  130 . That is to say, the dual color filter layer  130  preferably has the various thickness “t1/t2” according to its color, red, green, or blue.  
         [0077]    Now, with reference to FIGS. 9A to  9 F, a fabricating method for the color filter layer  130  according to the preferred embodiment is explained. At first as shown in FIG. 9A, on a transparent insulating substrate or upper substrate  110  (reference upper substrate  110  of FIG. 8), chromium oxide (CrO x ) and chromium (Cr) are sequentially deposited and patterned to form the black matrix  172 . The black matrix  172  has a patterned shape corresponding to the color filter layers, which will be formed subsequently.  
         [0078]    Then, as shown in FIG. 9B, a photo-polymerization polymer or organic insulating material is deposited on the upper substrate  110  to form the buffer layer  190 , which is transparent. Thereafter, as shown in FIG. 9C, the buffer layer  190  is patterned using a photolithography process such that a plurality of through holes  192  is formed. The through hole  192  corresponds to the transmissive portion  122   a  of FIG. 8. That is to say, the through hole  192  has the same size and position as the transmissive portion  122   a  of FIG. 8.  
         [0079]    Thereafter, as shown in FIG. 9D, a red color resin including a red dye is deposited and patterned on the buffer layer  190  to form red color filter layers  130 . For the sake of convenience, the color filter layer  130  of FIG. 8 is now defined as the red color filter. Due to the buffer layer  190 , the red color filter layer  130  has a stepped shape. As previously explained, the thickness ratio “t1/t2” the red color filter layer  130  is preferably 1.1 to 2.5.  
         [0080]    Thereafter, as shown in FIG. 9E, a green color resin including a green dye is deposited and patterned to form green color filter layers  132 . Subsequently in FIG. 9F, a blue color resin including a blue dye is subsequently deposited and patterned to form blue color filter layers  134 . Then, a transparent conductive material selected from a group consisting of indium tin oxide (ITO) or indium zinc oxide (IZO) is deposited on the red, green, and blue color filter layers  130 ,  132 , and  134  such that the common electrode  116  is formed. Though the black matrix  172  of FIGS. 9A to  9 E is employed for the preferred embodiment, it may be excluded for modifications of the preferred embodiment.  
         [0081]    [0081]FIG. 10 is a partially expanded view of FIG. 8. As shown, the first portion  130   a  of the color filter layer  130  is shrunken in a direction opposite to the transmissive portion  122   a . That is to say, when the color filter layer  130  is formed on the upper substrate  110  including the buffer layer  190 , portions of the color filter layer  130  are shrunken toward the upper substrate  110  due to a stepped surface of the upper substrate  110 . Therefore, The first portion  130   a  of the color filter layer  130  has a third thickness “t3”, which is smaller than the first thickness “t1” shown in FIG. 8 by a fourth thickness or shrinking depth “t4.” Relationships between the first to fifth thickness is expressed as: 
           t 2+ t 5= t 3+ t 4  (1) 
           t 1= t 3+ t 4  (2) 
         [0082]    , wherein a fifth thickness “t5” is a thickness of the buffer layer  190 .  
         [0083]    A thickness ratio “t3/t2” is preferably 1.1 to 2.5 such that the first and second portions  130   a  and  130   b  improve color properties, which is explained previously. Then, the third thickness “t3” of the first portion is preferably larger than the first thickness “t2” such that t3&gt;t2 or t3−t2&gt;0. Then, a relationship between the fourth and fifth thickness “t4” and “t5” is induced as follows: 
           t 3 −t 2 =t 5− t 4&gt;0, from the relationship  (1)  
         [0084]    , therefore, t5&gt;t4.  
         [0085]    That is to say, the buffer layer  190  preferably has a greater thickness than the shrinking thickness of the first portion  130   a.    
         [0086]    Still referring to FIG. 10, because of the shrinking thickness “t4”, the first liquid crystal portion  150   a  has a new cell gap, a third cell gap “d3”, which is greater than the first cell gap “d1” shown in FIG. 8. For the same reason explained previously, the third cell gap “d3” is about twice as the second cell gap “d2” of the second liquid crystal portion  150   b . Preferably, a cell gap ratio “d3/d2” is 1.5 to 2.5.  
         [0087]    It will be apparent to those skilled in the art that various modifications and variation can be made in the method of manufacturing a thin film transistor of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.