Patent Publication Number: US-2006001806-A1

Title: Liquid crystal display device

Description:
This application claims priority to Korean Patent Application No. 2004-0046131 filed on Jun. 21, 2004, and all the benefits accruing therefrom under 35 U.S.C §119, and the contents of which in its entirety are herein incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      (a) Field of the Invention  
      The present disclosure relates to a liquid crystal display device.  
      (b) Description of the Related Art  
      A liquid crystal display (“LCD”) device is a widely used example of a flat panel display device. An LCD device includes a lower panel and an upper panel having field-generating electrodes and a liquid crystal layer interposed between the lower and upper panels. The lower and upper panels along with the liquid crystal layer form a display panel of the LCD device. In order to display images, the LCD device controls a transmittance of light passing through the liquid crystal layer by realigning liquid crystal molecules disposed in the liquid crystal layer with voltages applied to the field-generating electrodes.  
      LCD devices are generally equipped with the lower and upper panels each having field-generating electrodes. Among widely used LCD device structures, pixel electrodes are typically arranged in a matrix form at the lower panel and one common electrode covers an entire surface of the upper panel. An image display of the LCD device is achieved by applying a voltage to each pixel electrode. In order to apply voltages to the pixel electrodes, a thin film transistor (TFT) for switching the voltages applied to the pixel electrodes is electrically connected to each pixel electrode. Also, a gate line for transmitting a signal to control the TFT and a data line for transmitting the voltages applied to pixel electrodes are installed at the display panel.  
      Depending on a light source employed, i.e. using a backlight or ambient light, LCD devices can be classified into different categories including, for example, a transmissive LCD device, a reflective LCD device and a transflective LCD device integrating a reflective mode and a transmissive mode.  
      Recently, a dual LCD device displaying images on both sides has been proposed. The dual LCD device, which is provided with a main liquid crystal display panel and a sub liquid crystal display panel, respectively, displays images on both sides.  
      However, the dual LCD device has problems in that although the main liquid crystal display panel and the sub liquid crystal display panel are installed at one LCD device, a backlight has to be installed for each of the main and sub liquid crystal display panels, thereby increasing a thickness, weight and power consumption of the dual LCD device.  
     SUMMARY OF THE INVENTION  
      A liquid crystal display device according to the present invention comprises a liquid crystal display panel, a light emitting unit and a light guide plate. The liquid crystal display panel is provided with a first substrate having a transmitting electrode and a reflecting electrode, a second substrate facing the first substrate with a gap disposed between the first and second substrates, and a liquid crystal layer disposed in the gap. The second substrate has a common electrode. The light emitting unit is disposed on the second substrate. The light emitting unit includes a lamp emitting light. The light guide plate transfers light emitted by the lamp to the liquid crystal display panel.  
      A display device is also provided that includes a first substrate, a second substrate, a liquid crystal layer and a light unit. The first substrate is disposed at a main window side of the display device. The second substrate is disposed opposite to the first substrate with respect to a gap between the first and second substrates. The second substrate is disposed at a sub window side of the display device. The liquid crystal layer is disposed in the gap. The light unit is disposed proximate to only one of the first and second substrates. The display device displays images at both the main window side and sub window side using light from the light unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a transflective type liquid crystal display device according to an exemplary embodiment of the present invention; and  
       FIG. 2  is a sectional view illustrating in details a lower substrate of  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention provides a dual liquid crystal display device, which uses a single liquid crystal display panel to display images on both sides of the liquid crystal display device.  
      Exemplary embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The present invention may, however, be embodied in different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
      In the drawings, thicknesses of layers, films, and regions are exaggerated for clarity. Like numerals refer to like elements throughout. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.  
       FIG. 1  is a sectional view of a transflective type liquid crystal display (LCD) device according to an exemplary embodiment of the present invention, and  FIG. 2  is a sectional view illustrating in detail a lower substrate of  FIG. 1 .  
      As shown in  FIG. 1 , a transflective type LCD device  510  (hereinafter referred to as “LCD device”) according to an exemplary embodiment of the present invention includes a light emitting unit  400  emitting a first light L 1  and a second light L 2 , and an LCD panel  350 , which is disposed proximate to an internal side of the light emitting unit  400 . The LCD device  510  displays images using the first light L 1 , the second light L 2 , or a third light L 3  supplied from an exterior of the LCD device  510 .  
      The LCD panel  350  is provided with an upper substrate  200 , a lower substrate  100  facing the upper substrate  200 , and a liquid crystal layer  300  disposed in a gap between the upper substrate  200  and the lower substrate  100 . The gap has a predetermined width d.  
      A first polarizing plate  120 , which is disposed on a lower part of the lower substrate  100 , polarizes the second light L 2  emitted from the light emitting unit  400  which has passed through the liquid crystal layer  300  of the LCD panel  350 .  
      A second polarizing plate  220  disposed on an upper part of the upper substrate  200 , polarizes the first light L 1  and the third light L 3 . The first light L 1  is emitted from the light emitting unit  400 , reflected by a reflecting electrode and projected back through a portion of the light emitting unit  400 .  
      The light emitting unit  400  is disposed on the LCD panel  350  and includes a lamp  410  emitting light and a light guide plate  420  transferring the first and second lights L 1  and L 2  projected from the lamp  410  to the LCD panel  350 .  
      The lamp  410  is surrounded on three sides by a reflective plate  430  that focuses the first and second lights L 1  and L 2  projected from the lamp  410  onto the light guide plate  420 .  
      As shown in  FIG. 1  and  FIG. 2 , the lower substrate  100  includes a first substrate  110 , a thin film transistor (TFT) array  114  disposed on the first substrate  110 , and a pixel electrode  117  disposed on the TFT array  114 .  
      The TFT array  114  includes a TFT  112  and a first protective layer  113  protecting the TFT  112 . The TFT  112  is formed of a gate electrode  112   a , a gate insulating layer  112   b , an active layer  112   c , an ohmic contact layer  112   d , a source electrode  112   e  and a drain electrode  112   f.    
      The gate electrode  112   a  is provided corresponding to a light shielding layer  211  disposed at a portion of a second substrate  210  of the upper substrate  200 . The gate insulating layer  112   b  is disposed on an entire surface of the first substrate  110  including where the gate electrode  112   a  is disposed.  
      The active layer  112   c  and the ohmic contact layer  112   d  are disposed on a portion of the gate insulating layer  112   b  corresponding to the gate electrode  112   a . The source electrode  112   e  and the drain electrode  112   f  are provided on the ohmic contact layer  112   d  and are spaced apart from each other at a certain distance.  
      In addition to the gate electrode  112   a , the source and drain electrodes  112   e  and  112   f  are also disposed corresponding to an area at which the light shielding layer  211  is disposed. Thus, the light shielding layer  211  protects the first and third lights L 1  and L 3  from being reflected by the gate electrode  112   a , the source electrode  112   e  and the drain electrode  112   f.    
      The first protective layer  113  disposed on the TFT  112  partially exposes the drain electrode  112   f  of the TFT  112 . The pixel electrode  117 , which is disposed on the first protective layer  113  and an exposed portion of the drain electrode  112   f , is electrically connected to the drain electrode  112   f.    
      The pixel electrode  117  is formed from a reflecting electrode  116  and a transmitting electrode  115 . The transmitting electrode  115  is made of, for example, indium tin oxide (ITO) or indium zinc oxide (IZO). The reflecting electrode  116  is made of a metal such as Aluminum-Neodymium (AlNd), is disposed on the transmitting electrode  115  and is connected to a portion of the drain electrode  112   f.    
      The reflecting electrode  116  has a transmitting window  116   a , which is a portion of the pixel electrode  117  where only the reflecting electrode  115  exists. The transmitting window  116   a  divides the lower substrate  100  into a reflection region RA corresponding to the portion of the pixel electrode where only the reflecting electrode  115  exists and a transmission region TA corresponding to a portion of the pixel electrode  117  where both the transmitting electrode  115  and the reflecting electrode exist. The reflecting electrode  116  is embossed to include lenses disposed in a pattern to increase a reflectivity of the first light L 1  and the third light L 3 .  
      The liquid crystal layer  300  is formed of, for example, twisted nematic liquid crystal.  
      The light shielding layer  211  and a color filter layer  212  are disposed on the upper substrate  210 , and a second protective layer  214  is disposed on the light shielding layer  211  and the color filter layer  212 .  
      The color filter layer  212  has red, green and blue color pixels (R, G and B), which are spaced apart from each other by a predetermined distance. The light shielding layer  211 , which is provided among the color pixels R, G and B, fixes boundaries of a region where each color pixel is formed, thereby improving color reappearance of each color pixel. The second protective layer  214  made of a photocrosslinkable material, is disposed on the color filter layer  212  and protects the color filter layer  212 .  
      A common electrode  215  is disposed on the second protective layer  214 . The common electrode  215  is made of a transparent conductive material and is disposed on the second protective layer  214  in a uniform thickness.  
      A portion of the second light L 2  emitted by the lamp  410  is reflected by an outer surface  421  of the light guide plate, and is projected through an inner surface of the light guide plate  422  and toward a main-window side indicated generally by arrow M through the liquid crystal layer  300  of the LCD panel  350  and the transmitting electrode  115 , thereby allowing a display of images at a first side (i.e. the main window side M) of the LCD device  510 . In other words, the LCD device  510  operates in a transmissive mode.  
      A portion of the first light L 1  emitted from the lamp  410  is reflected by the outer surface  421  of the light guide plate, passes through the liquid crystal layer  300  of the LCD panel  350 , and is reflected by the reflecting electrode  116 . Then, the portion of the first light L 1  passes through the light guide plate  420  and is projected to the exterior of the LCD device  510  toward a sub-window side indicated generally by arrow S, thereby allowing a display of images at a second side (i.e. the sub window side S) of the LCD device  510 . In other words, the LCD device  510  operates in a first reflective mode. The first reflective mode is preferably applied when the exterior is dark.  
      The third light L 3  passes through the light guide plate  420 , is reflected by the reflecting electrode  116  of the LCD panel  350 , passes through the light guide plate  420  again, and is projected to the exterior of the LCD device  510  toward the sub-window side S, thereby allowing the display of images at the second side of the LCD device  510 . In other words, the LCD device  510  operates in a second reflective mode, which is preferably applied when the exterior is bright.  
      As explained the above, the outer surface  421  of the light guide plate  420  reflects the first and second lights L 1  and L 2  emitted from the lamp  410 , transmits the third light L 3  in an incident direction, and transmits the first and third lights L 1  and L 3  reflected by the reflecting electrode  116  of the lower substrate  100  in an exiting direction.  
      Therefore, the sub window side S of the LCD panel  350  seen from the second of the LCD device  510  is used as a sub-window and, the main window side M of the LCD panel  350  seen from the first of the LCD device  510  is used as a main-window.  
      Thus, the main window side M of a single transflective LCD panel  350  is used in a transmissive mode and the sub window side S is used in a reflective mode, so that both sides of the LCD panel  350  may be used to display images.  
      The present invention provides a dual liquid crystal display device, which uses a single liquid crystal display panel and a single light emitting unit, thereby reducing thickness and weight of the liquid crystal display device while minimizing power consumption.  
      Although exemplary embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various changes and modifications may be affected therein by one of ordinary skill in the related art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.