Abstract:
An LCD device and a method for manufacturing the same are disclosed, wherein it is possible to reduce an ohmic contact between a reflective electrode and a transparent electrode and to simplify process steps. In the LCD device having first and second substrates and a liquid crystal layer between the first and second substrates, the LCD device includes a gate electrode and a first electrode of a storage capacitor on the first substrate; a first insulating film on the entire surface of the first substrate including the gate electrode; a semiconductor film, source/drain electrodes and a second electrode of the storage capacitor on the first insulating film; a second insulating film on the first insulating film including the source/drain electrodes; a reflective electrode on the second insulating film to connect the drain electrode with the second electrode of the storage capacitor; and a transparent electrode connected with the drain electrode on a third insulating film formed on the second insulating film including the reflective electrode.

Description:
RELATED APPLICATION  
         [0001]    The present application claims the benefit of Korean Patent Application No. P2000-56618 filed Sep. 27, 2000, which is herein fully incorporated by reference.  
         BACKGROUND OF THE INVENTION  
       Field of the Invention  
         [0002]    The present invention relates to a liquid crystal display device, and more particularly, to a method for manufacturing the same.  
         Background of the Related Art  
         [0003]    In general, a Cathode Ray Tube (CRT), one of display devices, has been widely used for monitors of information terminals and measuring instruments including a television. However, it was difficult for the CRT to actively adapt to miniaturization and lightweight due to its weight and size.  
           [0004]    A Liquid Crystal Display (LCD) device having a thin and small size has been actively developed in order to substitute for such a CRT. Recently, the LCD device is used as a flat panel display device. Thus, a demand of the LCD device is increasing consistently.  
           [0005]    Such an LCD device is largely classified into a transmissive LCD device and a reflective LCD device according to a light source. The transmissive LCD device using a back light as the light source can obtain a luminous picture in the dark outside. However, the transmissive LCD device has large size and bulk, and high power consumption due to the back light. The reflective LCD device does not use the back light, thereby obtaining low power consumption, small size and bulk. However, there is a limitation that the reflective LCD device cannot be used in the dark outside.  
           [0006]    To solve these problems, a transflective LCD device is disclosed, which can be used as the reflective LCD device or the transmissive LCD device at need.  
           [0007]    [0007]FIG. 1 a  and FIG. 1 b  are plan views of the transflective LCD device according to a related art. As shown in FIG. 1 a , a reflective electrode  3  is formed in a pixel region, and then a hole pattern  4  is formed in the reflective electrode  3 . In this structure, light partially passes through the hole pattern  4 . Or, as shown in FIG. 1 b , the reflective electrode  3  is formed at a predetermined portion of the pixel region, and then a transparent electrode  5  is formed in the rest of the pixel region.  
           [0008]    Although not described, “1” is a gate line, and “2” is a data line.  
           [0009]    A related art LCD device will be described with reference to the accompanying drawings.  
           [0010]    [0010]FIG. 2 is a sectional view of the related art LCD device. In FIG. 2, the LCD device includes an insulating substrate  11 , a gate electrode  13  and a first electrode  13   a  of a storage capacitor, a gate insulating film  15 , a semiconductor film  17  and source/drain electrodes  19  and  19   a , a second electrode  19   b  of the storage capacitor, a first passivation film  21 , a reflective electrode  23 , a second passivation film  25 , and a transparent electrode  29 . At this time, the gate electrode  13  and the first electrode  13   a  of the storage capacitor are formed on the insulating substrate  11 . The gate insulating film  15  is formed on the insulating substrate  11  including the gate electrode  13 , and then the semiconductor film  17 , source/drain electrodes  19  and  19   a , and the second electrode  19   b  of the storage capacitor are formed on the gate insulating film  15 . Subsequently, the first passivation film  21  is formed on an entire surface of the gate insulating film  15  including the second electrode  19   b , and the reflective electrode  23  is formed on the first passivation film  21 . The second passivation film  25  is formed on an entire surface of the first passivation film  21  including the reflective electrode  23 . Then, the transparent electrode  29  is connected with the reflective electrode  23  through the second passivation film  25 , and is connected with the drain electrode  19   a  and the second electrode  19   b  of the storage capacitor through the second passivation film  25  and the first passivation film  21 .  
           [0011]    A method for manufacturing the LCD device having such structure will be described with reference to FIG. 3 a  to FIG. 3 e.    
           [0012]    For reference, a TFT region (I) and a storage region (II) are simultaneously shown in the drawings.  
           [0013]    As shown in FIG. 3 a , a metal film using Al, Ta, MO or Al alloy is formed on the insulating substrate  11  by sputtering, and is patterned by photolithography, so that the gate electrode  13  is formed in the TFT region (I), and the first electrode  13   a  of the storage capacitor is formed in the storage region (II). Then, the gate insulating film  15  is formed on the entire surface of the insulating substrate  11  including the gate electrode  13  by chemical vapor deposition (CVD). At this time, the gate insulating film  15  is generally formed of silicon nitride (SiN x ) or silicon oxide (SiO x ). Although not shown, a gate pad is formed to have some distances with the first electrode  13   a  of the storage capacitor.  
           [0014]    As shown in FIG. 3 b , the semiconductor film is formed on the gate insulating film  15  by sputtering, and then is patterned by photolithography, so that the semiconductor film  17  is formed on the gate insulating film  15  above the gate electrode  13 . Then, the metal film is formed on the entire surface of the gate insulating film  15  including the semiconductor film  17  by sputtering. Subsequently, source/drain electrodes  19  and  19   a  are divided on the semiconductor film  17  by photolithography, and the second electrode  19   b  of the storage capacitor is formed. Although not shown, a data pad is formed on the gate insulating film  15  to have some distances with the second electrode  19   b  of the storage capacitor.  
           [0015]    As shown in FIG. 3 c , the first passivation film  21  is formed on the entire surface of the gate insulating film  15  including the second electrode  19   b  of the storage capacitor by CVD. Then, an aluminum film is formed on the first passivation film  21  by sputtering, and is patterned, thereby forming the reflective electrode  23  on the predetermined portion of the passivation film  21 . The second passivation film  25  is formed on the entire surface of the first passivation film  21  including the reflective electrode  23  by CVD.  
           [0016]    As shown in FIG. 3 d , the first and second passivation films  21  and  25  are selectively removed to expose the surfaces of the drain electrode  19   a , the reflective electrode  23  and the second electrode  19   b  of the storage capacitor, thereby forming contact holes  27   a ,  27   b  and  27   c.    
           [0017]    As shown in FIG. 3 e , an indium tin oxide (ITO) film is formed on the surface of the second passivation film  25  including the contact holes  27   a ,  27   b  and  27   c . Then, the transparent electrode  29  is formed to be electrically connected with the second electrode  19   b  of the storage capacitor and the reflective electrode  23 .  
           [0018]    Although not shown, a liquid crystal layer is formed between the insulating substrate  11  and an opposing substrate (not shown), so that manufacturing process steps are completed.  
           [0019]    However, the related art LCD device has the following problems.  
           [0020]    If the reflective electrode of aluminum is contacted with the transparent electrode of ITO, oxygen of ITO reacts with aluminum. Therefore, an undesired insulating film (Al 2 O 3 ) is formed at an interface between the reflective and transparent electrodes  23  and  29 . That is, an ohmic contact is remarkably increased in this portion, and then a driving voltage is not uniformly provided to the ITO and the reflective electrode. Accordingly, a parasitic capacitor is formed due to the insulating film formed between the reflective electrode and ITO, thereby resulting in a charged voltage negatively affecting the operation of pixels.  
         SUMMARY OF THE INVENTION  
         [0021]    Accordingly, the present invention is directed to an LCD device and a method for manufacturing the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0022]    An object of the present invention is to provide an LCD device and a method for manufacturing the same that reduces an ohmic contact between a reflective electrode and a transparent electrode and simplifies process steps.  
           [0023]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0024]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, in an LCD device having first and second substrates and a liquid crystal layer between the first and second substrates, the LCD device includes a gate electrode and a first electrode of a storage capacitor on the first substrate; a first insulating film on an entire surface of the first substrate including the gate electrode; a semiconductor film, source/drain electrodes and a second electrode of the storage capacitor on the first insulating film; a second insulating film on the first insulating film including the source/drain electrodes; a reflective electrode on the second insulating film to connect the drain electrode with the second electrode of the storage capacitor; and a transparent electrode connected with the drain electrode on a third insulating film formed on the second insulating film including the reflective electrode.  
           [0025]    In another aspect according to the first embodiment of the present invention, in a method for manufacturing an LCD having first and second substrates and a liquid crystal layer between the first and second substrates, the method includes the steps of forming a gate electrode and a first electrode of a storage capacitor on the first substrate; forming a first insulating film on an entire surface of the first substrate including the gate electrode; forming a semiconductor film, source/drain electrodes and a second electrode of the storage capacitor on the first insulating film; forming a second insulating film on the first insulating film including the source/drain electrodes; forming a reflective electrode connected with the drain electrode and the second electrode of the storage capacitor through the second insulating film; forming a third insulating film on the second insulating film including the reflective electrode; and forming a transparent electrode connected with the drain electrode through the second and third insulating films.  
           [0026]    In the LCD device and the method for manufacturing the same according to the first embodiment of the present invention, the reflective electrode is not directly connected with the transparent electrode of ITO, so that an undesired insulating film (e.g., Al 2 O 3 ) is not formed at an interface between the reflective and transparent electrodes. The transparent electrode is electrically connected with the drain electrode through a hole pattern formed in the reflective electrode.  
           [0027]    In still another aspect according to the second embodiment of the present invention, in an LCD device having first and second substrates and a liquid crystal layer between the first and second substrates, the LCD device includes a gate electrode and a first electrode of a storage capacitor on the first substrate; a first insulating film on an entire surface of the first substrate including the gate electrode; a semiconductor film, source/drain electrodes and a second electrode of the storage capacitor on the first insulating film; a second insulating film on the first insulating film including the source/drain electrodes; a reflective electrode on the second insulating film to connect the drain electrode with the second electrode of the storage capacitor through a contact hole; and a transparent electrode connected with the drain electrode on the second insulating film through the contact hole and extended to an upper portion of the reflective electrode.  
           [0028]    In further another aspect according to the second embodiment of the present invention, in a method for manufacturing an LCD having first and second substrates and a liquid crystal layer between the first and second substrates, the method includes the steps of forming a gate electrode and a first electrode of a storage capacitor on the first substrate; forming a first insulating film on an entire surface of the first substrate including the gate electrode; forming a semiconductor film, source/drain electrodes and a second electrode of the storage capacitor on the first insulating film; forming a second insulating film on the first insulating film including the source/drain electrodes; forming a reflective electrode connecting the drain electrode with the second electrode of the storage capacitor through the second insulating film; and forming a transparent electrode connected with the drain electrode through the second insulating film and extended to an upper portion of the reflective electrode.  
           [0029]    In the LCD device and the method for manufacturing the same according to the second embodiment of the present invention, the reflective electrode is primarily contacted with the drain electrode, and the transparent electrode is contacted with the drain and reflective electrodes without an additional process for forming the insulating film. Accordingly, even though an undesired insulating film may be formed at an interface between the reflective and transparent electrodes, an ohmic contact is not increased between the reflective and transparent electrodes due to equivalent electric potential provided by the drain electrode.  
           [0030]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0032]    [0032]FIG. 1 a  to FIG. 1 b  are plan views of a general transflective LCD device;  
         [0033]    [0033]FIG. 2 is a sectional view of a related art LCD device;  
         [0034]    [0034]FIG. 3 a  to FIG. 3 e  are sectional views showing manufacturing process steps of the related art LCD device;  
         [0035]    [0035]FIG. 4 is a sectional view of the LCD device according to a first embodiment of the present invention;  
         [0036]    [0036]FIG. 5 a  to FIG. 5 d  are sectional views showing manufacturing process steps of the LCD device according to the first embodiment of the present invention;  
         [0037]    [0037]FIG. 6 is a sectional view of the LCD device according to a second embodiment of the present invention; and  
         [0038]    [0038]FIG. 7 a  to FIG. 7 d  are sectional views showing manufacturing process steps of the LCD device according to the second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0040]    First embodiment  
         [0041]    [0041]FIG. 4 is a sectional view showing the structure of an LCD device according to the first embodiment of the present invention. FIG. 5 a  to FIG. 5 d  are sectional views showing manufacturing process steps of the LCD device according to the first embodiment of the present invention.  
         [0042]    For reference, FIG. 4 and FIG. 5 a  to FIG. 5 d  show a TFT region (I) and a storage region (II) simultaneously.  
         [0043]    As shown in FIG. 4, a first substrate  41  is formed, and then a gate electrode  43  and a first electrode  43   a  of a storage capacitor are formed on the first substrate  41  to provide a certain distance between the two electrodes  43  and  43   a . A first insulating film  45  is formed on the entire surface of the first substrate  41  including the gate electrode  43 . Then, a semiconductor film  47  is formed on the first insulating film  45  above the gate electrode  43 , and source/drain electrodes  49  and  49   a  are formed on the semiconductor film  47 . A second electrode  49   b  of the storage capacitor is formed on the first insulating film  45  above the first electrode  43   a  of the storage capacitor.  
         [0044]    Subsequently, a second insulating film  51  is formed on the first insulating film  45  including the second electrode  49   b  of the storage capacitor and patterned to define holes  53  through the second insulating film  51 . A reflective electrode  55  is formed on the second insulating film  51  to be connected with the drain electrode  49   a  and the second electrode  49   b  of the storage capacitor through the second insulating film  51 . Then, a third insulating film  57  is formed on the second insulating film  51  including the reflective electrode  55 , and patterned to define a hole  59  therethrough. A transparent electrode  61  is formed on the third insulating film  57  to be connected with the drain electrode  49   a  through the holes  53  and  59  of the third insulating film  57  and the second insulating film  51 .  
         [0045]    The first insulating film  45  is a gate insulating film, which is formed of a silicon nitride film or a silicon oxide film. The second insulating film  51  and the third insulating film  57  are formed of an organic insulating film, Benzocyclobutene(BCB) or an inorganic insulating film such as SiNx or SiO 2 .  
         [0046]    Although not shown, a liquid crystal layer is formed between the first substrate  41  and a second substrate (not shown).  
         [0047]    In the first embodiment of the present invention, the transparent electrode  61  is not directly contacted with the reflective electrode  55  but connected with the drain electrode  49   a  through the hole pattern that will be formed on the reflective electrode  61 . Therefore, an insulating film (e.g., Al 2 O 3 ) is not formed at an interface between the transparent and reflective electrodes  61  and  55 . As a result, an ohmic contact is reduced or is not increased between the two electrodes  61  and  55  and the operational characteristics of the LCD device is improved.  
         [0048]    A method for manufacturing the LCD device according to the first embodiment of the present invention will be described.  
         [0049]    As shown in FIG. 5 a , a metal film is formed on the first substrate  41  by sputtering or other existing techniques, and then the gate electrode  43  and the first electrode  43   a  of the storage capacitor are formed on the first substrate  41  by patterning the metal film. At this time, the metal film is formed of Al, Al alloy, Cr, Mo, Cu, or other known suitable metal materials.  
         [0050]    When the first insulating film  45  is formed on the entire surface of the first substrate  41  including the gate electrode  43 , the first insulating film  45  acts as a gate insulating film, which is formed of a silicon nitride film or silicon oxide film.  
         [0051]    As shown in FIG. 5 b , a material layer of amorphous silicon is formed on the first insulating film  45  and then patterned to form the semiconductor layer  47 . Then, the metal film is formed on the entire surface of the first insulating film  45  including the semiconductor film  45  by sputtering or other techniques, and is connected with the semiconductor film  47  by patterning the metal film. Subsequently, source/drain electrodes  49  and  49   a  are divided on the semiconductor film  47 , and the second electrode  49   b  of the storage capacitor is formed on the first insulating film  45  above the first electrode  43   a  of the storage capacitor. The source/drain electrodes  49  and  49   a  may be formed of a metal material such as Cu. In case of using Cu as the source/drain electrodes, a barrier film (not shown) is formed to improve the ohmic contact at the interface between the semiconductor film  47  and the source/drain electrodes  49  and  49   a.    
         [0052]    The second insulating film  51  is formed on the entire surface of the first insulating film  45  including the second electrode  49   b  of the storage capacitor. The contact hole  53  is formed to expose the drain electrode  49   a  and the second electrode  49   b  of the storage capacitor by photolithography. At this time, the second insulating film  51  is formed of an organic film such as BCB, a silicon nitride film, or a silicon oxide film.  
         [0053]    As shown in FIG. 5 c , the metal film such as an Al film is formed on the entire surface including the contact hole  53 , and then patterned to form the reflective electrode  55 , so that the drain electrode  49   a  is electrically connected with the second electrode  49   b  of the storage capacitor through the contact hole  53 .  
         [0054]    Subsequently, the third insulating film  57  is formed on the entire surface of the second insulating film  51  including the reflective electrode  55 , and then the third insulating film  57 , the reflective electrode  55  and the second insulating film  51  are selectively removed to expose the drain electrode  49   a , thereby forming the contact hole  59 .  
         [0055]    As shown in FIG. 5 d , the transparent electrode  61  of an indium tin oxide (ITO) is formed to be connected with the drain electrode  49   a  through the contact hole  59 . At this time, the third insulating film  57  is formed of an organic insulating film such as BCB or an inorganic insulating film such as a silicon film, a silicon nitride film, or a silicon oxide film.  
         [0056]    Although not shown, a second substrate is formed in the opposite to the first substrate  41 . Then, a liquid crystal film is formed between the first and second substrates, so that the process steps for manufacturing the LCD device according to the first embodiment of the present invention are completed.  
         [0057]    In the first embodiment of the present invention, the transparent electrode  61  is not directly connected with the reflective electrode  55  and is not flush with the reflective electrode  55 . Therefore, an insulating film is not formed at the interface between the two electrodes  55  and  61 .  
         [0058]    That is, the transparent electrode  61  is electrically connected with the drain electrode  55  below the reflective electrode  55  through the hole pattern formed on the reflective electrode  55 , so that the transparent electrode  61  and the reflective electrode  55  can be formed in different surfaces.  
         [0059]    Second Embodiment  
         [0060]    [0060]FIG. 6 is a sectional view of an LCD device according to a second embodiment of the present invention. FIG. 7 a  to FIG. 7 d  are sectional views showing manufacturing process steps of the LCD according to the second embodiment of the present invention, which show a TFT region (I) and a storage region (II) simultaneously.  
         [0061]    As shown in FIG. 6, in the LCD device according to the second embodiment of the present invention, a first substrate  71  is formed, and then a gate electrode  73  and a first electrode  73   a  of a storage capacitor are formed on the first substrate  71  to prove a certain distance between the two electrodes  73  and  73   a . A first insulating film  75  is formed on the entire surface of the first substrate  71  including the gate electrode  73  and the first electrode  73   a . Then, a semiconductor film  77  is formed on the first insulating film  75  above the gate electrode  73 , and source/drain electrodes  79  and  79   a  are formed on the semiconductor film  77 . A second electrode  79   b  of the storage capacitor is formed on the first insulating film  75  above the first electrode  73   a  of the storage capacitor.  
         [0062]    Subsequently, a second insulating film  81  is formed on the entire surface of the first insulating film  75  including the second electrode  79   b  of the storage capacitor. A reflective electrode  85  is formed in contact with the drain electrode  79   a  and the second electrode  79   b  of the storage capacitor through the second insulating film  81 . A transparent electrode  87  is in contact with the drain electrode  79   a  through the second insulating film  81  and is extended to the upper portion of the reflective electrode  85 .  
         [0063]    In the second embodiment of the present invention, the reflective electrode  85  is primarily in contact with the drain electrode  79   a , and the transparent electrode  87  is in contact with the drain electrode  79   a  and the reflective electrode  85 . In this case, even though an undesired insulating film (e.g., Al 2 O 3 ) may be formed at the interface between the reflective electrode  85  and the transparent electrode  87 , the reflective electrode  85  and the transparent electrode  87  are connected directly with the drain electrode  79   a , thereby obtaining an equivalent electric potential by the drain electrode  79   a . Accordingly, an ohmic contact between the reflective electrode  85  and the transparent electrode  87  is reduced or is not increased.  
         [0064]    A method for manufacturing the LCD device according to the second embodiment of the present invention will be described with reference to FIG. 7 a  to FIG. 7 d.    
         [0065]    As shown in FIG. 7 a , a metal film is formed on the first substrate  71  by sputtering or other techniques, and then the gate electrode  73  and the first electrode  73   a  of the storage capacitor are formed on the first substrate  71  by patterning the metal film. At this time, the metal film can be formed of Al, Al alloy, Cr, Mo, Cu or other known suitable metals.  
         [0066]    Subsequently, the first insulating film  75  is formed on the entire surface of the first substrate  71  including the gate electrode  73 . The first insulating film  75  is a gate insulating film, which can be formed of a silicon nitride film or silicon oxide film.  
         [0067]    As shown in FIG. 7 b , a semiconductor material layer made of, e.g., amorphous silicon is formed on the first insulating film  75  and then patterned to form the semiconductor film  77 . Then, a metal film is formed on the entire surface of the first insulating film  75  including the semiconductor film  77  by sputtering or other processes, and is connected with the semiconductor film  77 . Subsequently, the metal film is patterned so that source/drain electrodes  79  and  79   a  are formed on the semiconductor film  77 , and the second electrode  79   b  of the storage capacitor is formed on the first insulating film  75  above the first electrode  73   a  of the storage capacitor.  
         [0068]    The second insulating film  81  is formed on the entire surface of the first insulating film  75  including the second electrode  79   b  of the storage capacitor, and patterned by photolithography or other processes so that contact holes  83  are formed to expose the drain electrode  79   a  and the second electrode  79   b  of the storage capacitor.  
         [0069]    At this time, the source/drain electrodes  79  and  79   a  may be formed of Cu or other known materials. In case of using the Cu as source/drain electrodes, a barrier film (not shown) is formed to improve the ohmic contact at the interfaces between the semiconductor film  77  and the source/drain electrodes  79  and  79   a . The second insulating film  81  is formed of the organic insulating film such as BCB or an inorganic insulating film such as a silicon film, a silicon nitride film, or a silicon oxide film.  
         [0070]    As shown in FIG. 7 c , the metal film made of, e.g., Al is formed on the entire surface including the contact holes  83 , and then patterned to form the reflective electrode  85 , which is electrically connected with the drain electrode  79   a  and the second electrode  79   b  of the storage capacitor through the contact holes  83 .  
         [0071]    As shown in FIG. 7 d , a contact hole  88  is formed by removing a predetermined portion of the second insulating film  81  adjacent to the reflective electrode  85  to expose the drain electrode  79   a . Then, an ITO is formed on the entire surface of the second insulating film  81  including the contact hole  88 , and then patterned to form the transparent electrode  87 , which is in contact with the drain electrode  79   a  and extended over an upper portion of the reflective electrode  85 .  
         [0072]    Although not shown, a second substrate is formed opposite to the first substrate  71 . Then, a liquid crystal film is formed between the first and second substrates, so that the process steps for manufacturing LCD device according to the second embodiment of the present invention are completed.  
         [0073]    As aforementioned, the LCD device of the present invention has many advantages including the following.  
         [0074]    First, in some embodiments, the reflective electrode is not directly contacted with the transparent electrode, so that an undesired insulating film is not formed at the interface between the reflective and transparent electrodes. Therefore, the present invention prevents an increase of the ohmic contact at the interface portion.  
         [0075]    Furthermore, in other embodiments, the reflective electrode is primarily in contact with the drain electrode, and the transparent electrode is in contact with the drain electrode and the reflective electrode. In this event, even though an undesired insulating film (Al 2 O 3 ) may be formed at the interface between the reflective electrode and the transparent electrode, the reflective electrode and the transparent electrode are in contact with the drain electrode, thereby establishing an equivalent electric potential by the operation of the drain electrode. Accordingly, the present invention minimizes ohmic contact between the reflective electrode and the transparent electrode.  
         [0076]    The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses, methods and systems. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.