Abstract:
A liquid-crystal display device is provided. The liquid-crystal display device comprises a first substrate having a pixel electrode, a signal line, a scanning line, and a driver driving one of the signal line and the scanning line, a second substrate opposing the first substrate and having a common electrode, a liquid-crystal layer formed between the pixel electrode and the common electrode, and a first shield placed opposite the driver so as to shield an electromagnetic wave radiated from the driver.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a liquid-crystal display device, and more particularly, to a liquid-crystal display device displaying an image on a liquid-crystal panel. 
     2. Description of the Related Art 
     Currently, an active matrix liquid-crystal display device represented by a TFT (thin film transistor) liquid-crystal panel is expected to spread as a display device for general household TVs and OA apparatuses. This is because such an active matrix liquid-crystal display device can be easily made thin and light compared to a CRT, and at the same time, can display no poorer image than a CRT. 
     In light of the advantage of being thin and light, the active matrix liquid-crystal display device is expected to be applied, not only to a portable information device such as a note PC, but to various multimedia information devices. Besides, a polysilicon LCD realizing a narrow frame is expected to become prevalent with stronger measures being implemented against an EMI (electromagnetic interference). 
     A description will be given hereinbelow of a structure of such an active matrix liquid-crystal display device displaying one of the highest-quality images among flat panel displays.  FIG. 1  is an illustration showing a structure of the conventional liquid-crystal display device. As shown in  FIG. 1 , a conventional liquid-crystal display device  11  comprises a TFT substrate  1 , TFTs (thin-film transistors)  2 , signal lines  3 , scanning lines  4 , a common electrode substrate  5 , a common electrode  6 , a liquid-crystal layer  7 , an electrode lead-out line  8 , a signal-line drive circuit  9 , a scanning-line drive circuit  10 , and pixel electrodes  22 . The TFTs  2 , the signal lines  3 , the scanning lines  4 , the common electrode  6 , the pixel electrodes  22 , the liquid-crystal layer  7  provided between the pixel electrodes  22  and the common electrode  6 , compose a liquid-crystal panel. 
       FIG. 2  is a plan view showing a panel structure in the liquid-crystal display device  11  shown in FIG.  1 . As shown in  FIG. 2 , switching elements each consisting of the TFT  2 , the signal lines  3 , the scanning lines  4 , and the pixel electrodes  22  each connected to the TFT  2 , are formed on the TFT substrate  1 . Further, as shown in  FIG. 1 , the signal-line drive circuit  9  driving the signal lines  3 , the scanning-line drive circuit  10  driving the scanning lines  4 , and the electrode lead-out line  8  are formed on peripheral parts of the TFT substrate  1 . In addition, the common electrode  6  made of an ITO (a transparent electrode) or a color filter is formed on a glass substrate on the common electrode substrate  5 . 
     Also as shown in  FIG. 2 , the TFTs  2  and the pixel electrodes  22  are formed in the form of a matrix on the TFT substrate  1 . The signal line  3  supplies an image signal to the pixel electrode  22  via the TFT 2 . The scanning line  4  transmits a control signal to a gate of the TFT  2 , the control signal turning on/off the TFT  2  which is connected to the pixel electrode  22  so as to regulate writing of data to each pixel. It is noted that a unit like the liquid-crystal display device  11  that drives the signal lines  3  and the scanning lines  4  so as to display an image via the pixel electrodes  22  formed in the form of a matrix is referred to as an “active matrix liquid-crystal display device”. 
       FIG. 3  shows a cross-sectional structure of the liquid-crystal display device  11  shown in FIG.  1 . As shown in  FIG. 3 , the signal-line drive circuit  9  and other elements are formed on the TFT substrate  1 . The liquid-crystal layer  7  is provided between the common electrode  6  formed on the common electrode substrate  5  and the pixel electrodes  22  formed on the TFT substrate  1 . The TFT substrate  1  is electrically connected to the common electrode substrate  5  by a transfer  14   a . In addition, as shown in  FIG. 3 , a sealing portion  13  is provided between the TFT substrate  1  and the common electrode substrate  5  outside the transfer  14   a . The electrode lead-out line  8  and a protective film  12  are formed on a part of the TFT substrate  1  not covered by the common electrode substrate  5 . Signals are transmitted from the electrode lead-out line  8  to external devices by using a cable such as a flexible flat cable. 
     In the liquid-crystal display device  11  having the above-described structure, the TFTs  2  in a selected row are turned on so that an image-signal voltage applied to the signal line  3  is written to each of the pixel electrodes  22 , and the information is retained therein by keeping the electric charge until the next time the row is selected. In this course, the inclination of liquid-crystal molecules is so determined in accordance with the retained information as to regulate the amount of light transmission, enabling a gradation display, etc. Further, for a color display, an RGB color filter is used to mix lights. 
     The backside of such a liquid-crystal panel as above is provided with a surface light source called backlight. Recently, however, a reflective liquid-crystal panel not requiring this backlight attracts attention in the portable information device technology. The reflective liquid-crystal panel is provided with a layer referred to as a reflective electrode, and displays an image by reflecting externally supplied lights and transmits the lights through a liquid-crystal layer. 
     The above-described conventional liquid-crystal display device  11  has a problem that, since only an ITO (a transparent electrode) or an insulating layer is provided above the signal-line drive circuit  9  and the scanning-line drive circuit  10  formed on peripheral parts of the TFT substrate  1 , noises generated from these drive circuits cannot be reduced, which leads to an EMI (electromagnetic interference) especially in a high-frequency operation. 
     The same problem occurs with respect to the electrode lead-out line  8  shown in FIG.  1  and FIG.  3 . 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an improved and useful liquid-crystal display device in which the above-mentioned problems are eliminated. 
     A more specific object of the present invention is to provide a liquid-crystal display device in which noises (electromagnetic waves) emitted outwardly can be reduced. 
     In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a liquid-crystal display device comprising: 
     a first substrate having a pixel electrode, a signal line, a scanning line, and a driver driving one of the signal line and the scanning line; 
     a second substrate having a common electrode, the second substrate opposing the first substrate; 
     a liquid-crystal layer formed between the pixel electrode and the common electrode; and 
     a first shield placed opposite the driver so as to shield an electromagnetic wave radiated from the driver. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration showing a structure of a conventional liquid-crystal display device; 
         FIG. 2  is a plan view showing a panel structure in the liquid-crystal display device shown in  FIG. 1 ; 
         FIG. 3  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 1 ; 
         FIG. 4  is an illustration showing a structure of a liquid-crystal display device according to a first embodiment of the present invention; 
         FIG. 5  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 4 ; 
         FIG. 6  is an illustration showing a structure of a liquid-crystal display device according to a second embodiment of the present invention; 
         FIG. 7  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 6 ; 
         FIG. 8  is an illustration showing a structure of a liquid-crystal display device according to a third embodiment of the present invention; 
         FIG. 9  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 8 ; 
         FIG. 10  is an illustration showing a structure of a liquid-crystal display device according to a fourth embodiment of the present invention; 
         FIG. 11  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 10 ; 
         FIG. 12  is an illustration showing a structure of a liquid-crystal display device according to a fifth embodiment of the present invention; 
         FIG. 13  shows a cross-sectional structure of the liquid-crystal display device shown in  FIG. 12 ; 
         FIG. 14  is an illustration showing a structure of a liquid-crystal display device according to a sixth embodiment of the present invention; and 
         FIG. 15  shows a cross-sectional structure of the liquid-crystal display device shown in FIG.  14 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given, with reference to the drawings, of embodiments according to the present invention. Elements in the drawings that are identical or equivalent are referenced by the same reference marks. 
     Liquid-crystal display devices according to embodiments of the present invention are provided with augmented measures against an EMI (electromagnetic interference) by forming a layer of a shield electrode above the drive circuits and the electrode lead-out line formed on peripheral parts of the TFT substrate composing a liquid-crystal panel so as to reduce noises generated from these drive circuits. It is noted that stabilizing the electric potential of the shield electrode at a constant electric potential such as a ground potential enhances the shield effect, contributing effectively to the measures against the EMI. More specific descriptions will be given in the following. 
     [Embodiment 1] 
       FIG. 4  is an illustration showing a structure of a liquid-crystal display device  21  according to a first embodiment of the present invention.  FIG. 5  shows a cross-sectional structure of the liquid-crystal display device  21 . As shown in  FIG. 4 , the liquid-crystal display device  21  comprises the TFT substrate (a first substrate)  1 , the TFTs (thin-film transistors)  2 , the signal lines  3 , the scanning lines  4 , the common electrode substrate (a second substrate)  5 , the common electrode  6 , the liquid-crystal layer  7 , the electrode lead-out line  8 , the signal-line drive circuit  9 , the scanning-line drive circuit  10 , a ground electrode (a first shield)  15 , and the pixel electrodes  22 . The TFTs  2 , the signal lines  3 , the scanning lines  4 , the common electrode  6 , the pixel electrodes  22 , and the liquid-crystal layer  7  provided between the pixel electrodes  22  and the common electrode  6 , compose a liquid-crystal panel. 
     In the above-mentioned structure, switching elements each consisting of the TFT  2 , the signal lines  3 , the scanning lines  4 , and the pixel electrodes  22  each connected to the TFT  2 , are formed on the TFT substrate  1 . Further, the signal-line drive circuit  9  driving the signal lines  3 , the scanning-line drive circuit  10  driving the scanning lines  4 , and the electrode lead-out line  8  are formed on peripheral parts of the TFT substrate  1 . 
     On the other hand, unlike the conventional liquid-crystal display device  11  shown in  FIG. 1 , the common electrode substrate  5  of the liquid-crystal display device  21  according to the present first embodiment is provided with the ground electrode (a shield electrode)  15  formed above the signal-line drive circuit  9  and the scanning-line drive circuit  10 , along with the common electrode  6  made of an ITO (a transparent electrode) or a color filter. 
     However, as in the conventional liquid-crystal display device  11  shown in FIG.  1  and  FIG. 2 , the TFTs  2  and the pixel electrodes  22  are formed in the form of a matrix on the TFT substrate  1 . The signal line  3  supplies an image signal to the pixel electrode  22  via the TFT 2 . The scanning line  4  transmits a control signal to a gate of the TFT  2 , the control signal turning on/off the TFT  2  which is connected to the pixel electrode  22  so as to regulate writing of data to each pixel. 
     As shown in  FIG. 5 , the common electrode  6  is supplied with a common electrode potential from the TFT substrate  1  via the transfer  14   a . The ground electrode  15  is supplied with a ground potential from the TFT substrate  1  via a transfer (a voltage supplier)  14   b.    
     In the liquid-crystal display device  21  according to the present first embodiment, the ground electrode  15  functions as a shield against electromagnetic waves generated from the signal-line drive circuit  9  and the scanning-line drive circuit  10  so as to reduce electromagnetic waves leaked to the outside of the liquid-crystal display device  21 , contributing to the measures against the EMI. 
     [Embodiment 2] 
       FIG. 6  is an illustration showing a structure of a liquid-crystal display device  31  according to a second embodiment of the present invention.  FIG. 7  shows a cross-sectional structure of the liquid-crystal display device  31 . As shown in  FIG. 6 , the liquid-crystal display device  31  has the same structure as the liquid-crystal display device  21  according to the above-mentioned first embodiment, except that the common electrode substrate  5  (see also  FIG. 7 ) not having the ground electrode  15  is so provided as to cover the TFTs  2 , the pixel electrodes (not shown in the figure), the signal lines  3 , the scanning lines  4 , the signal-line drive circuit  9  and the scanning-line drive circuit  10 , and that a shield substrate (a third substrate)  16  (see  FIG. 7 ) having the ground electrode (a first shield)  15  is further provided above the electrode lead-out line  8 . The common electrode  6  is formed all across the common electrode substrate  5  not having the ground electrode  15 . 
     Additionally, as shown in  FIG. 7 , a flexible flat cable  20  is applied to the electrode lead-out line  8  by pressure, and thereafter, the shield substrate  16  having the ground electrode  15  formed by using aluminum or titanium is provided above the electrode lead-out line  8  and the part where the above-mentioned flexible flat cable  20  is applied to the electrode lead-out line  8 . The ground electrode  15  is supplied with a ground potential from the TFT substrate  1  via the transfer  14   b . The ground electrode  15  may be electrically connected to the TFT substrate  1  by a wire bonding, etc. in place of the transfer  14   b.    
     In this structure, since the shield substrate  16  is positioned outside a so-called display area in which the TFTs  2  and the pixel electrodes (not shown in the figure) are formed on the TFT substrate  1 , the shield substrate  16  does not cause a problem of narrowing the visible range of an image. Additionally, forming the ground electrode  15  by using aluminum or titanium as mentioned above can reduce a sheet resistance of the ground electrode  15  so as to further increase the shield effect. 
     In the liquid-crystal display device  31  according to the present second embodiment, the ground electrode  15  formed on the shield substrate  16  functions as a shield against electromagnetic waves generated from the electrode lead-out line  8  so as to reduce electromagnetic waves leaked outwardly from the liquid-crystal display device  31 ; this makes the measures against the EMI more effective. 
     Additionally, according to the liquid-crystal display device  31  of the present second embodiment, the shield substrate  16  is a separate and independent component from the TFT substrate  1  and the common electrode substrate  5  and thus can be manufactured separately and independently. Also, the shield substrate  16  can be combined with a conventional liquid-crystal display device easily into the liquid-crystal display device according to the present second embodiment. 
     [Embodiment 3] 
       FIG. 8  is an illustration showing a structure of a liquid-crystal display device  41  according to a third embodiment of the present invention.  FIG. 9  shows a cross-sectional structure of the liquid-crystal display device  41 . As shown in  FIG. 8 , the liquid-crystal display device  41  has the same structure as the liquid-crystal display device  31  according to the above-mentioned second embodiment, except that the common electrode substrate  5  is provided above the TFTs  2 , the pixel electrodes (not shown in the figure), the signal lines  3 , and the scanning lines  4 , and that a shield substrate (a third substrate)  26  having the ground electrode (a first shield)  15  is provided above the signal-line drive circuit  9  and the scanning-line drive circuit  10 . 
     As shown in  FIG. 9 , the ground electrode  15  is supplied with a ground potential from the TFT substrate  1  via the transfer  14   b , as in the liquid-crystal display device  31  according to the above-mentioned second embodiment. 
     In the liquid-crystal display device  41  according to the present third embodiment, the ground electrode  15  formed on the shield substrate  26  functions as a shield against electromagnetic waves generated from the signal-line drive circuit  9  and the scanning-line drive circuit  10  so as to reduce electromagnetic waves leaked from the liquid-crystal display device  41  outwardly; this makes the measures against the EMI more effective. 
     Additionally, as in the liquid-crystal display device  31  according to the above-mentioned second embodiment, the shield substrate  26  is a separate and independent component from the TFT substrate  1  and the common electrode substrate  5  and thus can be manufactured separately and independently. Also, the shield substrate  26  can be combined with a conventional liquid-crystal display device easily into the liquid-crystal display device according to the present third embodiment. 
     [Embodiment 4] 
       FIG. 10  is an illustration showing a structure of a liquid-crystal display device  51  according to a fourth embodiment of the present invention.  FIG. 11  shows a cross-sectional structure of the liquid-crystal display device  51 . As shown in  FIG. 10 , the liquid-crystal display device  51  has the same structure as the liquid-crystal display device  41  according to the above-mentioned third embodiment, except that the shield substrate  16  (see  FIG. 11 ) having the ground electrode  15  is further provided above the electrode lead-out line  8 . 
     As shown in  FIG. 11 , the ground electrodes  15  formed on the shield substrates  16  and  26  are supplied with a ground potential from the TFT substrate  1  via the transfers  14   b , as in the liquid-crystal display devices  31  and  41  according to the above-mentioned second and third embodiments. 
     In the liquid-crystal display device  51  according to the present fourth embodiment, the ground electrode  15  (a first shield) formed on the shield substrate (a third substrate)  16  and the ground electrode  15  (a second shield) formed on the shield substrate (a fourth substrate)  26  function as shields against electromagnetic waves generated from the electrode lead-out line  8 , the signal-line drive circuit  9  and the scanning-line drive circuit  10  so as to reduce electromagnetic waves leaked from the liquid-crystal display device  51  outwardly; this contributes to the measures against the EMI effectively. In addition, the shield substrates  16  and  26  are a separate and independent component from the TFT substrate  1  and the common electrode substrate  5  and thus can be manufactured separately and independently. 
     [Embodiment 5] 
       FIG. 12  is an illustration showing a structure of a liquid-crystal display device  61  according to a fifth embodiment of the present invention.  FIG. 13  shows a cross-sectional structure of the liquid-crystal display device  61 . As shown in  FIG. 12 , the liquid-crystal display device  61  has the same structure as the liquid-crystal display device  51  according to the above-mentioned fourth embodiment, except that a unitary shield substrate (a third substrate)  36  (see  FIG. 13 ) having the ground electrode (a shield)  15  formed unitarily thereon is provided above the electrode lead-out line  8 , the signal-line drive circuit  9  and the scanning-line drive circuit  10 . In other words, in the liquid-crystal display device  61  according to the present fifth embodiment, the shield substrates  16  and  26  of the liquid-crystal display device  51  according to the above-mentioned fourth embodiment are unitarily formed. 
     As shown in  FIG. 13 , the ground electrode  15  formed on the shield substrate  36  is supplied with a ground potential from the TFT substrate  1  via the transfer  14   b , as in the liquid-crystal display device  51  according to the above-mentioned fourth embodiment. 
     In the liquid-crystal display device  61  according to the present fifth embodiment, the ground electrode  15  formed on the shield substrate  36  functions as a shield against electromagnetic waves generated from the electrode lead-out line  8 , the signal-line drive circuit  9  and the scanning-line drive circuit  10  so as to reduce electromagnetic waves leaked from the liquid-crystal display device  61  outwardly; this contributes to the measures against the EMI effectively. 
     Additionally, in the liquid-crystal display device  61  according to the present fifth embodiment, the shield substrate has a larger area such that a larger number of the transfers  14   b  can be provided between the shield substrate  36  and the TFT substrate  1 ; this increases the shield effect further. 
     [Embodiment 6] 
       FIG. 14  is an illustration showing a structure of a liquid-crystal display device  71  according to a sixth embodiment of the present invention.  FIG. 15  shows a cross-sectional structure of the liquid-crystal display device  71 . As shown in  FIG. 14 , the liquid-crystal display device  71  has the same structure as the liquid-crystal display device  21  according to the above-mentioned first embodiment, except that the shield substrate (a third substrate)  16  (see  FIG. 15 ) having the ground electrode (a second shield)  15  is further provided above the electrode lead-out line  8 . 
     As shown in  FIG. 15 , the ground electrode  15  formed on the shield substrate  16  is supplied with a ground potential from the TFT substrate  1  via the transfer  14   b , as in the liquid-crystal display devices  31  and  51  according to the above-mentioned second and fourth embodiments. 
     In the liquid-crystal display device  71  according to the present sixth embodiment, the ground electrodes  15  formed on the common electrode substrate  5  and the shield substrate  16  function as shields against electromagnetic waves generated from the signal-line drive circuit  9 , the scanning-line drive circuit  10 , and the electrode lead-out line  8  so as to reduce electromagnetic waves leaked from the liquid-crystal display device  71  outwardly; this contributes to the measures against the EMI effectively. 
     Besides, in the liquid-crystal display devices according to the above-described first to sixth embodiment, when the ground electrode  15  is formed of the same material as the common electrode  6 , the ground electrode  15  and the common electrode  6  can be formed at the same time by the same process. Thus, the liquid-crystal display devices can be achieved without increasing the number of manufacturing steps. 
     Also, as mentioned above, forming the ground electrode  15  by using aluminum or titanium can reduce a sheet resistance of the ground electrode  15  so as to further increase the shield effect. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 2001-024594 filed on Jan. 31, 2001, the entire contents of which are hereby incorporated by reference.