Abstract:
A liquid crystal display (LCD) includes a liquid crystal panel including first and second substrates, and a liquid crystal layer filled with liquid crystals between the first and second substrates, a backlight module irradiating light on the liquid crystal panel, a driver controlling the liquid crystals to adjust an amount of light transmission, and a second common electrode formed on at least one of the first and second substrates, the second common electrode having a characteristic of a high heat emitting resistance.

Description:
This application claims the benefit of Korean Patent Application No. 2003-062763, filed on Sep. 8, 2003, 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), and more particularly, to an LCD that is capable of constantly maintaining response time of liquid crystal regardless of temperature, and a method of fabricating the same. 
     2. Description of the Related Art 
     Today, with rapid development of information technology, a flat panel display having advantages of slimness, lightweight and low power consumption is in great demand. The LCD is one such flat panel display that has superior visibility, lower power consumption and lower heat radiation when compared with a cathode ray tube (CRT) having the same screen size. For this reason, the LCD is widely used in hand-held devices, computer monitors and televisions. The LCD, along with plasma display panel (PDP) or field emission display (FED) is expected to be the next generation displays. 
     The LCD usually includes two substrates, each having an electrode for generating an electric field and facing each other, and a liquid crystal layer interposed therebetween. When a voltage is applied to the electrodes of the respective substrates, the LCD utilizes the electric field to control liquid crystal molecules to display images. 
       FIG. 1  is a schematic plan view showing an LCD according to the related art, and  FIG. 2  is an enlarged cross-sectional view showing a region A of the LCD of  FIG. 1 . Referring to  FIGS. 1 and 2 , the related art LCD includes a liquid crystal panel  10 , a backlight module (not shown) disposed at a lower portion of the liquid crystal panel  10  to irradiate light to the liquid crystal panel  10 , and a driver  11  disposed at an outer region of the liquid crystal panel  10  to drive the liquid crystal panel  10 . 
     The liquid crystal panel  10  includes a first substrate  15  and a second substrate  17  that are spaced apart by a predetermined interval and face each other. Also, a liquid crystal layer (not shown) is interposed between the first and second substrates  15 ,  17 . 
     The first substrate  15  is provided with gate lines and data lines arranged in a matrix. A plurality of thin film transistors (TFTs) acting as switching elements are formed at intersections of the gate and the data lines. Each of the TFTs has a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a pixel electrode. The pixel region is defined by the TFT and the pixel electrode. Also, a common electrode line  16  is formed on the first substrate  15  to supply a predetermined common voltage. 
     The second substrate  17  is formed with a black matrix (BM) (not shown), a color filter layer  18  and a common electrode  19 . The color filter layer  18  includes red (R), green (G) and blue (B) color filters that are arranged in sequence. The black matrix may be provided among the respective color filters in order to prevent light from being irradiated to an adjacent color filter. The common electrode  19  may be formed on the whole surface of the color filter layer  18 . 
     The liquid crystal panel  10  is provided with a seal pattern  13 , at corners of an outer region of which a conductive layer  14  is formed to connect the common electrode line  16  with the common electrode  19 . Accordingly, a common voltage that is applied to the common electrode line  16  can be equally supplied to the common electrode  19  through the conductive layer  14 . 
     The backlight module includes a lamp, a light guide plate for guiding light from the lamp to the liquid crystal panel  10 , a reflective plate disposed under the light guide plate to reflect the light irradiated to a lower portion of the light guide plate, and a diffusion sheet disposed on the light guide plate to diffuse the light irradiated to the liquid crystal panel  10 . 
     The driver  11  of  FIG. 1  includes a printed circuit board (PCB) on which drive circuits are mounted to generate predetermined drive signals, and a drive integrated circuit (IC)  12  connected between the PCB and the liquid crystal panel  10  to supply the drive signals to the liquid crystal panel  10 . A package method of the drive IC  12  may be classified into a chip on glass (COG), a tape carrier package (TCP), a chip on film (COF), etc.  FIG. 1  is an exemplary view of the TCP. 
     In the LCD as constructed above, the TFTs of the liquid crystal panel  10  are turned on in response to the drive signals from the driver, and the data signals are applied to the pixel electrode, thereby forming a predetermined electric field. While variation of the liquid crystals is changed due to the electric field, an amount of light transmission is controlled to display images. 
     The liquid crystals may be typically used at a temperature ranging from −40° C. to 90° C. When the LCD is driven at a room temperature, the liquid crystals have no influence on the response time. However, a problem occurs when the LCD is driven at the low temperature in that the response time of the liquid crystals tend to be slow at a low temperature. Accordingly, if the LCD is driven at the low temperature, the response time of the liquid crystals is degraded, thus generating a flicker, or the like. As a result, picture quality is degraded. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an LCD that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an LCD and a method of fabricating the same, which are capable of maintaining a constant response time of liquid crystals regardless of temperature. 
     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. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an LCD, which comprises a liquid crystal panel including first and second substrates, and a liquid crystal layer filled with liquid crystals between the first and second substrates, a backlight module irradiating light on the liquid crystal panel, a driver controlling the liquid crystals to adjust an amount of light transmission, and a second common electrode formed on one of the first and second substrates, the second common electrode having a characteristic of high heat emitting resistance. 
     In another embodiment of the present invention, an LCD comprises a first substrate including a thin film transistor, a second substrate including a black matrix, a color filter layer, a first common electrode and a second common electrode, the first electrode having heat emitting resistance lower than the second common electrode, a seal pattern bonding the first and second substrates by a predetermined interval, a first common electrode line formed on the first substrate corresponding to an outer region of the seal pattern, a first conductive layer connected between the first common electrode line and the first common electrode, a second common electrode line formed on an outermost region of the first substrate, and a second conductive layer connected between the second common electrode line and the second common electrode. 
     According to another aspect of the present invention, there is provided a method of fabricating an LCD comprising forming a second common electrode on a substrate by depositing a first transparent layer, forming a black matrix and a color filter layer on the second common electrode, and forming a first common electrode on the color filter layer by depositing a second transparent layer, the first transparent layer having lower heat emitting resistance than that of the second transparent layer. 
     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 
       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 embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  is a schematic plan view of an LCD according to the related art; 
         FIG. 2  is an enlarged view showing a region A of an outer region of the LCD of  FIG. 1 ; 
         FIG. 3  is a schematic plan view of an LCD according to the present invention; 
         FIG. 4  is an enlarged view illustrating a region B of an outer region of the LCD of  FIG. 3 ; and 
         FIGS. 5A to 5C  are cross-sectional views illustrating sequential procedures of fabricating the LCD according to the present invention. 
     
    
    
     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 like parts. 
       FIG. 3  is a schematic plan view of an LCD according to the present invention, and  FIG. 4  is an enlarged view illustrating a region B of an outer region of the LCD of  FIG. 3 . Referring to  FIGS. 3 and 4 , the LCD includes a liquid crystal panel  30 , a backlight module (not shown) disposed at a lower portion of the liquid crystal panel  30  to irradiate light to the liquid crystal panel  30 , and a driver  31  disposed at an outer region of the liquid crystal panel  30  to drive the liquid crystal panel  30 . 
     As shown in  FIG. 4 , the liquid crystal panel  30  includes a first substrate  36  and a second substrate  39  that are spaced apart by a predetermined interval and face each other. Also, a liquid crystal layer (not shown) interposed between the first and second substrates  36 ,  39 . 
     The first substrate  36  is provided with gate and data lines that are arranged in matrix. Thin film transistors (TFTs) acting as switching elements are formed at intersections of the gate and the data lines. Each of the TFTs has a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a pixel electrode. A pixel region is defined by the TFT and the pixel electrode. Also, the first substrate  36  is provided with a first common electrode line  37  and a second common electrode line  38  to supply a predetermined common voltage. The first and second common electrode lines  37 ,  38  are spaced apart by a predetermined interval and may be formed on the same layer. 
     The second substrate  39  is provided with a second common electrode  42 , a color filter layer  40  and a first common electrode  41  that are sequentially deposited thereon. The color filter layer  40  includes red (R), green (G) and blue (B) color filters that are arranged in sequence. A black matrix is provided among the respective color filters in order to prevent light from being irradiated to an adjacent color filter. The second common electrode  42  may be formed on the whole surface of the second substrate  39 . The first common electrode  41  may be formed on the whole surface of the color filter layer  40 . It is preferable that the second common electrode  42  has a characteristic of high heat emitting resistance. Also, both the first and second common electrodes  41 ,  42  may be formed of the same transparent conductive layer, such as an indium tin oxide (ITO) layer or the like. 
     When the same common voltage is applied to both the first and second common electrodes  41 ,  42 , the second common electrode  42  emits higher heat than the first common electrode  41 , thereby increasing the temperature of the LCD. 
     According to the present invention, the common voltage is applied to the first common electrode  41  when the LCD is driven at a room temperature. Therefore, a small amount of heat is emitted in the first common electrode  41  and the liquid crystals are reacted stably, thereby maintaining a constant response time. 
     In the present invention, when the LCD is driven at the low temperature, the common voltage is applied to the second common electrode  42  to generate high heat, thereby increasing temperature of the LCD. Therefore, the response time of the liquid crystals at the low temperature can be maintained at a constant similar to that of the room temperature response time, and thus prevent the response time of the liquid crystals from being degraded due to the low temperature. 
     The liquid crystal panel  30  is provided with a seal pattern  33 , at corners of an outer region of which a first conductive layer  34  is formed to connect the first common electrode line  37  with the first common electrode  41 . A second conductive layer  35  is formed at the outermost region of the liquid crystal panel  30  and spaced apart from the seal pattern  33  by a predetermined interval, to connect the second common electrode line  38  with the second common electrode  42 . The first and second conductive layers  34 ,  35  may be formed of Ag dot, silver paste or the like. At least one or more of the first and second conductive layers  34 ,  35  may be provided. 
     The seal pattern  33  is provided to bond the first substrate  36  with the second substrate  39 . Liquid crystals are injected into a space defined by the first and second substrates  36 ,  39  and the seal pattern  33 . 
     Generally, the first substrate  36  is wider than the second substrate  39 . A region for displaying an image can be defined by the seal pattern  33 . The driver  31  is disposed around and connected to the first substrate  36 . Accordingly, the common voltage that is supplied to the first common electrode line  37  can be simultaneously supplied to the first common electrode  41  through the first conductive layer  34 . Also, the common voltage that is supplied to the second common electrode line  38  can be simultaneously supplied to the second common electrode  42  through the second conductive layer  35 . 
     The backlight module includes a lamp, a light guide plate for guiding light from the lamp to the liquid crystal panel  30 , a reflective plate disposed under the light guide plate to reflect the light irradiated to a lower portion of the light guide plate, and a diffusion sheet disposed on the light guide plate to diffuse the light irradiated to the liquid crystal panel  30 . 
     The driver  31  of  FIG. 3  includes a printed circuit board (PCB) on which drive circuits are mounted to generate predetermined drive signals, and a drive integrated circuit (IC)  32  connected between the PCB and the liquid crystal panel  30  to supply the drive signals to the liquid crystal panel  30 . A package method of the drive IC  32  may be classified into a chip on glass (COG), a tape carrier package (TCP), and a chip on film (COF).  FIG. 3  is an exemplary view of the TCP. 
     In the LCD as constructed above, the liquid crystal panel  30  is driven in response to the drive signals from the driver  31 . At this point, the driver  31  supplies external data signals to the liquid crystal panel  30 . In other words, if the drive signals are supplied to the gate lines arranged on the first substrate  36 , the data signals are applied to the pixel electrodes under control of the TFTs and a corresponding common voltage is applied at the same time, thus forming an electric field. As a result, variation of the liquid crystals is changed and a predetermined image is displayed. 
     In a case where the LCD is driven at the room temperature, the common voltage is applied to the first common electrode line  37  and the first common electrode  41 . On the contrary, in a case where the LCD is driven at the low temperature, the common voltage is applied to the second common electrode line  38  and the second common electrode  42 . Thus, the second common electrode  42  has a characteristic of higher heat emitting resistance than the first common electrode  41 , so that a considerable heat is generated in the second common electrode  42 . As a result, temperature of the LCD is increased enough to maintain the response time constant, instead of degrading the response time due to the low temperature. 
     For this operation, a temperature sensor or the like, which can sense a surrounding temperature, may be attached to a predetermined portion of the LCD. Based on the temperature sensed by the temperature sensor, it can be determined that the common voltage is applied to the first common electrode  41  or the second common electrode  42 . For example, if the sensed temperature is the room temperature, the common voltage is applied to the first common electrode  41 . On the contrary, if the sensed temperature is the low temperature, the common voltage is applied to the second common electrode  42 . 
       FIGS. 5A to 5C  are cross-sectional views illustrating sequential procedures of fabricating the LCD according to the present invention. Referring to  FIG. 5A , after a transparent glass substrate  51  is cleaned, an indium tin oxide (ITO) layer is deposited on the whole area of the glass substrate  51  using a sputtering process, thereby forming a second common electrode  52 . The ITO layer has good characteristics in transmittance, conductivity, chemical and thermal stability, and a relatively high heat emitting resistance. 
     Referring to  FIG. 5B , a chrome-based or carbon-based organic material is deposited on the second common electrode  52  using the sputtering process and is patterned using a mask, thereby forming a black matrix  53 . At this point, the black matrix  53  on the second common electrode  52  is formed in a matrix configuration, thereby preventing leakage of light irradiated to the black matrix  53 . 
     After the black matrix  53  is formed, a color filter layer  54  is patterned using a color resist, which reproduces colors when light is irradiated thereto. In other words, a red color resist is coated over the whole area of the second common electrode  52 , thereby completely covering the black matrix  53 . Then, only a specific region (for example, red region) of an upper portion of the coated color resist is exposed using a mask and a partial development is performed. After that, the red color resist whose photochemical structure is changed due to the exposure is developed using a developer and the developed red color resister is hardened to form a red color filter. Since the color resist generally has a negative characteristic, an unexposed region is removed. Then, a green color filter and a blue color filter are formed by repeating the above process of forming the red color filter. 
     Referring to  FIG. 5C , an indium tin oxide (ITO) layer is deposited on the whole area of the color filter layer  54  using a sputtering process, thereby forming a first common electrode  55 . The ITO layer has good characteristics in transmittance, conductivity, chemical and thermal stability, and a relatively high heat emitting resistance. Through the above processes, the second substrate  39  of  FIG. 4  is thus formed. 
     As described above, the LCD of the present invention includes the first common electrode having a low heat emitting characteristic and the second common electrode having a high heat emitting characteristic. Thus, when the LCD is driven at the room temperature, the common voltage is applied to the first common electrode to generate a low heat. As a result, the response time of the liquid crystals can be maintained constant. Meanwhile, when the LCD is driven at the low temperature, the common voltage is applied to the second common electrode to generate a high heat. As a result, the temperature of the LCD is increased, thereby preventing the response time of the liquid crystals from being degraded due to the low temperature. 
     In other words, even when the LCD is driven at the low temperature, a constant response time can be maintained regardless of changes in temperature by increasing temperature of the LCD through the common electrode having a high heat emitting characteristic. Accordingly, the degradation in the response time of the liquid crystals due to the low temperature is prevented, thereby preventing the degradation of the picture quality due to the flicker or the like. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present 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.