Patent Publication Number: US-7719502-B2

Title: Liquid crystal display device and television receiver set

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on Japanese priority application No. 2004-153924 filed on May 24, 2004, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to liquid crystal display devices and more particularly to a liquid crystal display device of vertical alignment (VA) mode. 
     A liquid crystal display device is a display device having the feature of compact size and small electric power consumption. Thus, a liquid crystal display device has been used extensively for various portable information processing apparatuses, particularly laptop computers or cellular phones. On the other hand, much progress has been made with regard to the performance of liquid crystal display device in the past, including the response speed and contrast ratio, and a liquid crystal display device is used nowadays also for replacing conventional CRT display apparatuses of desktop computers and workstations. 
     Further, in recent years, there are increasing instances in which a liquid crystal display device is used for displaying images in a television set ranging from a large screen television set to a compact portable television set. In the case of using a liquid crystal display device for a television set, there is imposed a demand that the liquid crystal display device is capable of displaying a motion picture with high speed. 
     Meanwhile, a liquid crystal display device of the vertical alignment mode, particularly the liquid crystal display device of MVA mode is used extensively for the display devices of computers and cellular phones in view of its excellent contrast ratio and wide viewing angle characteristics. It should be noted that the liquid crystal display device of MVA mode or MVA liquid crystal display device is a liquid crystal display device in which there are formed plural domains of different tilting directions of liquid crystal molecules in a single pixel region. 
     Thus, there is a natural demand of using such a liquid display device of MVA mode also for the display of television images. 
       FIGS. 1A and 1B  are diagrams showing the principle of a MVA liquid crystal device  10  proposed by the inventor of the present invention, wherein  FIG. 1A  shows the liquid crystal display device  10  in the non-activated state in which there is applied no driving electric field to a liquid crystal layer  12 , while  FIG. 1B  shows the same liquid crystal display device  10  in an activated state in which a driving electric field is applied to the liquid crystal layer  12 . 
     Referring to  FIG. 1A , the liquid crystal layer  12  is held between a glass substrate  11 A and a glass substrate  11 B, wherein the glass substrate  11 A and  11 B form a liquid crystal panel together with the liquid crystal layer  12 . 
     On each of the glass substrates  11 A and  11 B, there are formed respective alignment films not illustrated, wherein the alignment films control the pointing direction of the liquid crystal molecules of the liquid crystal layer  12  such that the liquid crystal molecules are aligned in a direction generally perpendicular to the liquid crystal layer  12  in the non-activated state in which no drive electric field is applied to the liquid crystal layer  12 . 
     In this state, the optical beam incident to the liquid crystal display device undergoes no substantial rotation of its polarization plane as it passes through the liquid crystal layer, and thus, the optical beam incident to the liquid crystal layer  12  through a polarizer is interrupted by an analyzer, provided that the polarizer and the analyzer are disposed above and below the liquid crystal panel in a crossed Nicol relationship. 
     In the activated state of  FIG. 1B , on the other hand, the liquid molecules are tilted as a result of the applied electric field, and because of this, the optical beam incident to the liquid crystal layer undergoes rotation of the polarization plane thereof. As a result, the optical beam incident to the liquid crystal layer  12  through the polarizer passes also through the analyzer. 
     Further, in the liquid crystal display device  10  of  FIGS. 1A and 1B , there are formed projecting patterns  13 A and  13 B respectively on the glass substrates  11 A and  11 B so as to extend parallel with each other, wherein the projecting patterns  13 A and  13 B impose localized constraint with regard to the tilting direction of the liquid crystal molecules particularly at the time of transition from the non-activated state to the activated state. With this, the response speed of the liquid crystal display device  10  is improved. 
     By forming such projecting patterns  13 A and  13 B, not only the response speed of the liquid crystal display device  10  is improved, but there are also formed plural domains of different tilting directions of the liquid crystal molecules in the liquid crystal layer. Thereby, the viewing angle characteristics of the liquid crystal display device are improved significantly. 
     [Patent Reference 1] Japanese Laid-Open Patent Application 2002-107730 gazette 
     [Patent Reference 2] Japanese Laid-Open Patent Application 2002-357830 gazette 
     SUMMARY OF THE INVENTION 
     Thus, with a liquid crystal display device of MVA type, nearly ideal black representation is realized in the non-activated state thereof, and thus, a high contrast ratio is achieved. Further, because of the constraint imposed by the projecting patterns  13 A and  13 B with regard to the tilting direction of the liquid crystal molecules, a high response speed is achieved for such a liquid crystal display device, which is designed for displaying primarily static images. 
     On the other hand, in the case of displaying motion picture images by using such an MVA liquid crystal display device, there arises a problem, in view of the mechanism of transition of the liquid crystal molecules in such an MVA liquid crystal display device in that the transition occurs first in the region in the vicinity of the projecting patterns  13 A and  13 B and then propagates to the region of the liquid crystal layer other than the protecting patterns  13 A and  13 B, in that the response speed is not sufficient for such a purpose of displaying motion picture images as in the case of television. For example, one may encounter the problem that the displayed images are blurred. 
     Hereinafter, this problem of response speed will be explained for the example of the conventional MVA liquid crystal display device  30  shown in  FIG. 2 . 
     Referring to  FIG. 2 , the liquid crystal display device  30  is an active-matrix device and includes a TFT glass substrate  31 A carrying thereon a large number of thin film transistors (TFTs) and transparent pixel electrodes each cooperating with one TFT, and an opposing glass substrate  31 B opposing the TFT glass substrate  31 A and carrying thereon an opposing electrode, wherein a liquid crystal layer  31  is confined between the substrates  31 A and  31 B by a seal member  31 C. In the illustrated liquid crystal display device, the pointing direction of the liquid crystal molecules is changed selectively in the liquid crystal layer  31  in correspondence to a selected pixel electrode driven by a corresponding TFT. Further, it should be noted that there are disposed a polarizer  31   a  and an analyzer  31   b  at respective outer sides of the glass substrates  31 A and  31 B in a crossed Nicol relationship. In addition, there are formed alignment films at the inner sides of the glass substrates  31 A and  31 B in contact with the liquid crystal layer  31 , wherein the alignment films restrict the pointing direction of the liquid crystal molecules in the direction generally perpendicular to the plane of the liquid crystal layer  31  in the non-activated state thereof. 
     For the liquid crystal layer  31 , it is possible to use a liquid crystal having a negative dielectric anisotropy marketed from Merck Ltd, Japan, while it is possible to use a vertical alignment film provided by JSR Corporation for the foregoing alignment films. In a typical example, the substrates  31 A and  31 B are assembled by using suitable spacers so that the liquid crystal layer  31  held therebetween has a thickness of about 4 μm. 
       FIG. 3A  shows the liquid crystal display device of  FIG. 2  in a cross-sectional view, while  FIG. 3B  shows a part of the TFT glass substrate  31 A in an enlarged scale. 
     Referring to  FIG. 3A , it can be seen that there are formed pixel electrodes  34  on the lower glass substrate  31 A constituting the TFT substrate in electrical connection to corresponding TFTs  31 T, wherein the pixel electrodes  34  are covered with a vertical molecular alignment film  35 . Further, an opposing electrode  36  is formed uniformly on the upper glass substrate  31 B, and the opposing electrode  36  is covered by another molecular alignment film  37 . 
     Thereby, the liquid crystal layer  33  is held between the substrates  31 A and  31 B in the state that the liquid crystal layer  33  makes a contact with the alignment films  35  and  37 . 
     Referring to  FIG. 3B , the glass substrate  31 A carries thereon a large number of pad electrodes  33 A to which a scanning signal is supplied, wherein it can be seen that a large number of scanning electrodes  33  extend therefrom. Further, the glass substrate  31 A carries thereon a large number of pad electrodes  32 A to which a video signal is supplied and a large number of signal electrodes  32  extend therefrom in the direction generally perpendicular to the extending direction of the scanning electrodes  33 . Further, TFTs  31 T are formed at the intersections of the scanning electrodes  33  and the signal electrodes  32 . Further, on the substrate  31 A, there are formed transparent pixel electrodes  34  in correspondence to the TFTs  31 T, wherein each of the TFTs  31 T is selected by a scanning signal on the corresponding scanning electrode  33  and drives the cooperating transparent pixel electrode  34  formed of ITO, or the like, by video signal on the corresponding signal electrode  32 . 
     In the non-activated state in which no drive voltage is applied to the transparent pixel electrode  34 , the liquid crystal molecules are aligned in the liquid crystal display device  30  in the direction generally perpendicular to the plane of the liquid crystal layer  31  and a dark representation is achieved as a result of the function of the polarizer  31   a  and the analyzer  31   b  disposed in the crossed Nicol relationship. On the other hand, in the activated state in which a drive voltage is applied to the transparent pixel electrode  34 , the liquid crystal molecules are aligned generally horizontally, and a white representation is achieved. 
     As shown in  FIG. 3A , there are formed cutout patterns  34 A in the pixel electrode  34 , and the alignment film  35  is formed so as to cover the cutout patterns  34 A. Further, there are provided projecting patterns  36 A on the upper electrode  36  as a result of patterning of a monomer film such as a resist film. 
     Thereby, it should be noted that the projecting patterns  36 A cause localized tilting in the liquid crystal molecules similarly to the projecting patterns  13 B of  FIGS. 1A and 1B . Further, the cutout patterns  34 A also induce localized modification of electric field distribution and cause localized titling in the liquid crystal molecules similarly to the projecting patterns shown in  FIGS. 1A and 1B . 
       FIG. 4  shows the construction of a single pixel electrode  34  formed on the substrate  31 A in detail. 
     Referring to  FIG. 4 , it can be seen that the signal electrodes  32  and the scanning electrode  33  extend in the crossing relationship on the substrate  31 A and that a TFT  31 T and a pixel electrode  34  cooperating therewith are formed in correspondence to each intersection of the electrodes  32  and  33 . Further, it can be seen that auxiliary capacitance  34 C (Cs) is formed parallel to each of the scanning electrodes  33  in the construction of  FIG. 4 . 
     In  FIG. 4 , it will be noted that the pixel electrode  34  shown by a mat pattern is divided into regions A and B, and each of the regions A and B is formed with the cutout patterns  34 A shown in white such that the cutout patterns  34 A extend parallel with each other in correspondence to the construction of  FIGS. 1A and 1B  explained before. 
     Further, in  FIG. 4 , there are also shown the projecting patterns  36 A formed on the glass substrate  31 B, in addition to the pixel electrode  34  formed on the substrate  31 A. 
       FIG. 5  shows the transition of transmittance of the MVA liquid crystal display device  30  of  FIG. 2  caused in correspondence to the transition of state of the liquid crystal display device  30  from the dark state in which no drive signal is supplied to the white stated in which a drive signal of ±2.5V is supplied. In  FIG. 4 , the horizontal axis represents the time while the vertical axis represents the transmissivity. 
     Referring to  FIG. 5 , it should be noted that no drive signal is supplied to the pixel electrode  34  in the first interval T 1  and the liquid crystal display device  30  is in the dark state. On the other hand, in the interval T 2 , a drive voltage of 2.5V is applied in the form of a rectangular waveform signal, and the liquid crystal display device  30  causes transition to the white state. Thereby, it should be noted that each of the rectangular waves has a duration t 1  corresponding to one frame. In the case of displaying an image of 60 frames per second, the duration t 1  of one frame should be 16.7 ms. 
     Thus, in the case the liquid crystal display device  30  is driven like this, it takes a time of several frames until the transmittance fully goes up, while this means that the display cannot follow the change of the images to be displayed in the case the gradation of the image to be displayed is changed within this interval. 
     Further, from  FIG. 5 , it will be seen that the liquid crystal display device  30  resumes its black state quickly when the drive voltage has returned to zero in the interval T 3  that follows the interval T 2 . 
     In order to improve the response speed at the time of transition of state of the liquid crystal display device, it has been practiced in the art to use a so-called overdrive technology, in which the magnitude of the drive voltage pulse is increased beyond a predetermined value corresponding to the desired gradation temporarily at the time of starting the driving or in the first frame of the gradation transition. This overdrive technology is used in various liquid crystal display devices, and it is also possible to use the overdrive technology in the MVA liquid crystal display device of  FIG. 3 . 
       FIG. 6  shows the transition of transmittance observed in the same MVA liquid crystal display device  30  used in the experiment of  FIG. 5 , for the case the overdrive technology is used, in which the magnitude of the drive voltage pulse of the first frame of the interval T 2 , which follows the interval T 1  of 0V drive voltage, is set to +3.1V, and the a nominal drive voltage of ±2.5V is supplied thereafter in the remaining interval T 2 . In  FIG. 6 , it should be noted that the drive voltage is returned again to 0V in the interval T 3  that follows the interval T 2 . 
     Referring to  FIG. 6 , it can be seen that a very sharp increase of transmittance is achieved at the beginning of the interval T 2  as a result of the use of the overdrive technology. On the other hand, it can be seen also that the transmittance swings for a while over the duration of several frames that follow the sharp transition, and it can be seen that it takes time until a constant stable transmittance is reached. 
     It should be noted that the relationship of  FIGS. 5 and 6  is first discovered by the inventor of the present invention in the investigation that constitutes the foundation of the present invention. 
     It is believed that such instability of transmittance reflects the instability of alignment of the liquid crystal molecules caused in the liquid crystal layer with the overdriving. 
     In the liquid crystal display device of the MVA type, in which the tilting of the liquid crystal molecules first started in the vicinity of the projecting patterns  13 A and  13 B or  36 A or in the vicinity of the cutout patterns  34 A propagates to the entire liquid crystal layer, such instability of alignment of the liquid crystal molecules raises a serious problem. 
     For example, in the case there has been caused variation of the transmittance that continues for several frames as in the example of  FIG. 6 , there appears a ghost in the display of motion pictures. 
     Meanwhile, in the art of liquid crystal display device, it should be noted that each pixel holds an image over the duration of one frame, contrary to the case of a CRT display device. Thus, representation of motion pictures with such a liquid crystal display device tends to cause the problem of afterimages or tailing of images when viewed by human eyes. 
     Thus, in order to display natural motion picture images with such a liquid crystal display device, it is practiced to use a technology in which the display screen is divided into plural regions each having a corresponding backlight unit, and carry out a quasi-vertical scanning of backlight by switching the backlight units one after another during one frame representation. 
     On the other hand, according to the experiments made by the inventor of the present invention and constituting the foundation of the present invention, it was discovered that such switching of the backlight unit deteriorates the quality of represented images even further when used with the MVA liquid crystal display devices for displaying motion pictures. The foregoing problem of oscillation or swinging of the transmittance causes this further deterioration of image quality when the MVA liquid crystal display device is used with the overdrive technology and with the backlight switching technology. 
     According to a first aspect of the present invention, there is provided a liquid crystal display device, comprising: 
     a first substrate carrying a first electrode; 
     a first alignment film formed on said first substrate so as to cover said first electrode; 
     a second substrate carrying a second electrode and opposing said first substrate; 
     a second alignment film formed on said second substrate so as to cover said second electrode; 
     a liquid crystal layer sandwiched between said first and second substrates via respective alignment films; 
     a first polarizer having a first optical absorption axis and disposed outside said first substrate; 
     a second polarizer having a second optical absorption axis perpendicular to said first optical absorption axis and disposed outside said second substrate; and 
     a drive unit applying a drive voltage signal to said first and second electrodes, 
     said first and second alignment films causing liquid crystal molecules of said liquid crystal layer to align in a direction generally perpendicular to a plane of said liquid crystal layer in a non-activated state of said liquid crystal display device in which no drive voltage is applied across said first and second electrodes, 
     said first electrode constituting a pixel electrode including therein regions characterized by different tilting directions of said liquid crystal molecules, 
     said liquid crystal molecules being inclined in each of said plural regions in a predetermined direction pertinent to said region over generally entirety of a display region of said liquid crystal display device in said non-activated state thereof, 
     said drive unit setting the voltage of a drive voltage signal, in the case of displaying a first gradation image having a first gradation and subsequently and continuously displaying a second gradation image having a second gradation, such that a magnitude of said drive voltage signal is increased larger than a predetermined voltage of said drive signal for said second gradation during a first frame interval of displaying said second gradation image. 
     In another aspect of the present invention, there is provided a television receiver set, comprising: 
     a signal processing circuit supplied with a high frequency signal including a video signal and a synchronization signal, said signal processing circuit extracting said video signal and said synchronization signal therefrom; 
     a drive circuit producing a drive voltage signal from said video signal; and 
     a liquid crystal display device driven by said drive voltage signal, 
     said liquid crystal display device comprising: 
     a first substrate carrying a first electrode; 
     a first alignment film formed on said first substrate so as to cover said first electrode; 
     a second substrate carrying a second electrode and opposing said first substrate; 
     a second alignment film formed on said second substrate so as to cover said second electrode; 
     a liquid crystal layer sandwiched between said first and second substrates via respective alignment films; 
     a first polarizer having a first optical absorption axis and disposed outside said first substrate; 
     a second polarizer having a second optical absorption axis perpendicular to said first optical absorption axis and disposed outside said second substrate; and 
     a drive unit applying a drive voltage signal to said first and second electrodes, 
     said first and second alignment films causing liquid crystal molecules of said liquid crystal layer to align in a direction generally perpendicular to a plane of said liquid crystal layer in a non-activated state of said liquid crystal display device in which no drive voltage is applied across said first and second electrodes, 
     said first electrode constituting a pixel electrode including therein regions characterized by different tilting directions of said liquid crystal molecules, 
     said liquid crystal molecules being inclined in each of said plural regions in a predetermined direction pertinent to said region over generally entirety of a display region of said liquid crystal display device in said non-activated state thereof, 
     said drive unit setting the voltage of a drive voltage signal, in the case of displaying a first gradation image having a first gradation and subsequently and continuously displaying a second gradation image having a second gradation, such that a magnitude of said drive voltage signal is increased larger than a predetermined voltage of said drive signal for said second gradation during a first frame interval of displaying said second gradation image. 
     According to the present invention, the problem of swinging of transmittance occurring in the case the overdrive technology is applied to an MVA liquid crystal display device is effectively eliminated by causing the liquid crystal molecules to tilt over generally entire display area in the tilting direction pertinent to the display area. By tilting (pretilting) the liquid crystal molecules over generally entire display area in the tilting direction pertinent to the display area in the non-activated state of the liquid crystal display device, the liquid crystal molecules change the tilting angle thereof substantially simultaneously to a tilting angle corresponding to the desired gradation at the respective locations of the liquid crystal molecules. 
     Such pretilting of the liquid crystal molecules in the non-activated state of the liquid crystal display device can be easily realized by forming a polymer layer on the vertical alignment film, by optically curing a photocuring monomer composition having a liquid crystal skeleton. Further, by providing a backlight unit behind the liquid crystal display device and by illuminating different regions of the liquid crystal display device consecutively and sequentially by using the backlight unit, it becomes possible to achieve high-performance display of motion pictures characterized by high contrast ratio, wide viewing angle and little after images or blurs. 
     Further, there occurs no degradation of display image quality even in the case the quasi-vertical scanning caused by switching of the backlight unit is applied simultaneously with the overdriving. It should be noted that there has been caused severe degradation of display image quality of motion pictures when such quasi-vertical scanning has been used in the conventional MVA liquid crystal display devices in combination with the overdrive technology. 
     Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are diagrams explaining the principle of an MVA liquid crystal display device; 
         FIG. 2  is a diagram showing the construction of an MVA liquid crystal display device according to the related art; 
         FIGS. 3A and 3B  are diagrams showing the construction of the MVA liquid crystal display device of  FIG. 2 ; 
         FIG. 4  is a diagram showing the pixel construction of the MVA liquid crystal display device of  FIG. 2 ; 
         FIG. 5  is a diagram explaining the problems of the MVA liquid crystal display device of  FIG. 2 ; 
         FIG. 6  is another diagram explaining the problem of the MVA liquid crystal display device of  FIG. 2 ; 
         FIG. 7  is a diagram showing the construction of the liquid crystal display device according to a first embodiment of the present invention; 
         FIG. 8  is another diagram showing the construction of the liquid crystal display device of  FIG. 7 ; 
         FIGS. 9A and 9B  are further diagrams showing the construction of the liquid crystal display device of  FIG. 7 ; 
         FIG. 10  is a diagram showing the pixel construction used with the liquid crystal display device of  FIG. 7 ; 
         FIGS. 11A-11C  are diagrams showing the fabrication process of the liquid crystal display device of  FIG. 7 ; 
         FIG. 12  is a diagram explaining the overdrive of the liquid crystal display device of  FIG. 7 ; 
         FIG. 13  is a diagram explaining the effect of the present invention; 
         FIG. 14  is a diagram showing the construction of a drive circuit used with the liquid crystal display device of  FIG. 7 ; 
         FIGS. 15A and 15B  are diagrams explaining the backlight control used with the liquid crystal display device of  FIG. 7 ; 
         FIG. 16  is a diagram showing the pixel construction according to a second embodiment of the present invention; 
         FIGS. 17A and 17B  are diagrams showing the construction of the liquid crystal display device according to a third embodiment of the present invention; and 
         FIG. 18  is a diagram showing the construction of a television receiver set according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 7  shows the construction of a MVA liquid crystal display device  40  according to a first embodiment of the present invention. 
     Referring to  FIG. 7 , the liquid crystal display device  40  is formed of a liquid crystal display panel  50  of MVA type, a backlight unit  60  disposed behind the liquid crystal display panel  50  and a drive circuit  70  supplied with image data and driving the liquid crystal display panel  50  with a drive voltage signal corresponding to the image data, wherein there is provided a diffusion plate  62  between the backlight unit  60  and the liquid crystal display panel  50 . The backlight unit  60  is formed of light sources  61 A- 61 D and respective cooperating optical scatter plates  60   a - 60   d . Further description of the backlight  60  will be given later. 
     The light emitted from the backlight unit  60  is modulated by the liquid crystal display panel  50  and is emitted to the front side of the liquid crystal display panel  50 . 
       FIG. 8  shows the construction of the liquid crystal display panel  50 . 
     Referring to  FIG. 8 , the liquid crystal display panel  50  is an active-matrix liquid crystal display apparatus and includes a TFT glass substrate  51 A carrying thereon a large number of thin film transistors (TFTs) and transparent pixel electrodes cooperating with the TFTs and an opposing glass substrate  51 B provided over the TFT substrate  51 A and carrying thereon an opposing electrode, wherein a liquid crystal layer  51  is confined between the substrates  51 A and  51 B by a seal member  51 C. 
     In the illustrated liquid crystal panel, the pointing direction of the liquid crystal molecules is modulated selectively in the liquid crystal layer  51  by selectively driving a selected transparent pixel electrode via a corresponding TFT. 
     Further, it should be noted that there are disposed a polarizer  51   a  and an analyzer  51   b  at the respective outer sides of the glass substrates  51 A and  51 B in a crossed Nicol state. 
     Further, there are formed alignment films (not shown) at the respective inner sides of the glass substrates  51 A and  51 B, wherein the alignment films restrict the alignment of the liquid crystal molecules such that the liquid crystal molecules are aligned in the direction generally perpendicular to the plane of the liquid crystal layer  51  in the non-activated state of the liquid crystal display device. 
     For the liquid crystal layer  51 , it is possible to use a liquid crystal having negative dielectric anisotropy marketed from Merck Japan, Ltd. 
     Further, for the alignment films, it is possible to use a vertical alignment film marketed from JSR Corporation. In a typical example, the substrates  51 A and  51 B are assembled by using a suitable spacer such that the liquid crystal layer  51  is formed with the thickness of about 4 μm. 
       FIG. 9A  shows the liquid crystal display panel  50  of  FIG. 8  in a cross-sectional view, while  FIG. 9B  shows a part of the TFT glass substrate  51 A in an enlarged view. 
     Referring to  FIG. 9A , a number of pixel electrodes  35  are formed in a row and column formation each in electrical connection with a corresponding TFT  51 T not illustrated, wherein the pixel electrode  54  is covered with the vertical alignment film  55 . Similarly, the upper glass substrate  51 B is covered uniformly by an opposing electrode  56 , wherein the opposing electrode  56  is covered with another vertical alignment film  57 . Thereby, the liquid crystal layer  51  is sandwiched between the substrates  51 A and  51 B in the state contacting with the vertical alignment films  55  and  57 . 
     Referring to  FIG. 9B , the glass substrate  51 A carries thereon a large number of pad electrodes  53 A each supplied with a scanning signal and a large number of scanning electrodes  53  extending therefrom, while the glass substrate  51 A further carries thereon a large number of pad electrodes each supplied with a video signal and a large number of signal electrodes  52  extending therefrom such that the extending direction of the scanning electrodes and the extending direction of the signal electrodes  52  intersect generally perpendicularly with each other. 
     At each intersection of the scanning electrodes  53  and the signal electrodes  52 , there is formed a TFT  51 T, wherein a transparent pixel electrode  54  is formed further on the substrate  51 A in correspondence to each of the TFTs  51 T. Thus, each TFT  51 T is selected by a scanning signal supplied to a corresponding scanning electrode  53 , and the TFT thus selected drives the cooperating transparent pixel electrode  54  made of ITO, or the like, by the video signal, which is a driving voltage signal supplied to the corresponding signal electrode  52 . 
     Because the liquid crystal molecules are aligned generally perpendicularly to the plane of the liquid crystal layer  51  in the liquid crystal display panel  50  in the non-activated state thereof in which no drive voltage is applied to the transparent pixel electrode  54 , the liquid crystal display panel  50  provides a dark representation due to the function of the polarizer  51   a  and the analyzer  51   b , while in the activated state in which a drive voltage is applied to the transparent pixel electrode  54 , the liquid crystal molecules are aligned generally horizontally, and the liquid crystal display panel provides a white representation. 
     As will be explained later, the molecular alignment films  55  and  56  have their respective surfaces formed with polymer layers  55   a  and  57   a , wherein the polymer layers  55   a  and  57   a  induces slight tilting in the liquid crystal molecules in the liquid crystal layer  31  with regard to the plane of the liquid crystal layer  51 . Explanation about the polymer layers  55   a  and  57   a  will be given later. 
     Further, as shown in  FIG. 8A , there are formed cutout patterns  54 A in the pixel electrode  54 , and the alignment film  55  and the polymer layer  55   a  are formed so as to cover the cutout patterns  54 A. 
     Further, it should be noted that there are formed projection patterns  56 A on the upper electrode  56  by patterning of a monomer film such as a resist film. Thereby, the projecting patterns  56 A induce a localized tilting of the liquid crystal molecules similar to the case of the projecting pattern  36 A of  FIG. 3A , while the foregoing cutout patterns  54 A also induces similar localized modulation of the electric field, resulting in similar localized tilting of the liquid crystal molecules. 
     In the construction of  FIG. 9A , it is also possible to provide one or more phase compensation films between the glass substrate  51 A and the polarizer  51   a  and/or between the glass substrate  51 B and the analyzer  51   b . Such a phase compensation film may be an optically uniaxial phase compensation film in which the refractive indices n x  and n y  in the plane of the liquid crystal layer  51  are larger than the refractive index n z  in the direction in which the optical wave propagates. 
       FIG. 10  shows the construction of one pixel electrode  54  formed on the substrate  51 A in detail. 
     Referring to  FIG. 10 , there extend the signal electrodes  52  and the scanning electrodes on the substrate  51 A in a crossing relationship, and the TFTs  51 T and cooperating pixel electrodes  54  are formed in correspondence to the intersections of the electrodes  52  and  53 . Further, it can be seen in  FIG. 10  that there is formed an auxiliary electrode  54 C (Cs) so as to extend parallel with the scanning electrode  53 . 
     In  FIG. 10 , it should be noted that the pixel electrode  54 , shown with mat pattern, is divided into a region A and a region B, wherein the cutout patterns  54 A shown with a white strip extend on each of the regions A and B parallel with each other in correspondence to the construction of  FIG. 4 . 
     Further, it should be noted that  FIG. 10  also shows the projecting patterns  56 A formed on the glass substrate  51 B, in addition to the pixel electrode  54  on the substrate  31 A. 
     Next, the process of formation of the polymer layers  55   a  and  57   a  mentioned before will be explained with reference to  FIGS. 11A-11C  together with their functions. 
     Referring to  FIG. 11A , there is introduced a photocuring monomer composition  51 M having a liquid crystal skeleton, such as a liquid crystal mono acrylate monomer USL-001-K1 marketed from Dainippon Ink and Chemicals, Inc., is introduced with a concentration range of 0.1-3 wt %. 
     Next, in the step of  FIG. 11B , a drive voltage is applied across the electrodes  54  and  56  such that tilting is caused in the liquid crystal molecules  51 L. In this stage, it should be noted that the direction of tilt of the liquid crystal molecules  51 L is determined by the cutout patterns  54 A formed in the pixel electrode  54  or by the projecting patterns  56  formed on the opposing electrode  56 . Further, in the state of  FIG. 11B , ultraviolet radiation is applied to the liquid crystal layer  51  in this state and causes curing in the photocuring monomer composition  51 M. 
     As a result, the polymer layer  55   a  is formed on the surface of the veridical alignment film  55  and the polymer layer  57   a  is formed on the surface of the vertical alignment film  57  in correspondence to the state of  FIG. 9A , wherein it should be noted that the polymer layers  55   a  and  57   a  memorize the tilting direction of the liquid crystal layer  51 L in the state of  FIG. 11B , and thus, the liquid crystal molecules  51 L are held in the slightly tilted state toward the foregoing tilting direction from the direction perpendicular to the plane of the liquid crystal layer  51 . 
     It should be noted that the polymer layers  55   a  and  57   a  are formed respectively on the entirety of the surfaces of the alignment films  55  and  57 , and thus, the tilting of the liquid crystal molecules  51 L occurs promptly when tilting the liquid crystal molecules  51 L by applying a drive voltage across the electrodes  54  and  56 . Thereby, the response speed of the liquid crystal panel  50  is improved significantly. 
     In the present embodiment, in which the response speed of the liquid crystal display panel  50  is thus improved, attempt is made to improve the response speed further in the case the gradation of the represented images is changed by conducting the overdriving shown in  FIG. 12 . 
       FIG. 12  is a diagram showing the drive voltage signal waveform produced by the drive circuit  70  of  FIG. 7  and applied between the electrodes  54  and  55 . 
     Referring to  FIG. 12 , the drive voltage signal has a rectangular waveform changing the polarity thereof alternately about a central voltage Vc, wherein one period of each rectangular wave corresponds to one frame (16.7 mS). 
     In the example of  FIG. 12 , it should be noted that the displayed image maintains a first gradation for the first interval T 1  and then causes a transition to a second gradation in the second interval T 2 , and in correspondence to this, the drive voltage signal is changed from the first interval T 1  in which the drive voltage signal takes the value of ±V 1  with regard to the central voltage Vc to the second interval T 2  in which the drive voltage signal takes the value of ±V 2 , wherein the present embodiment increases the magnitude of the drive voltage to Vo at the moment of transition of the gradation, and hence in the first frame of the interval T 2 . 
     It should be noted that the magnitude of the overdrive voltage Vo is determined according to the equation Vo=A×V 2 , in which a coefficient A is multiplied to the magnitude of the drive voltage signal V 2  for the second interval T 2 , wherein the coefficient A is determined as a function of the drive voltage V 1  in the previous interval T 1  and the magnitude of the voltage V 2  of the current interval T 2  and the temperature T. 
       FIG. 13  shows the transmittance of the liquid crystal panel for the case the display is changed from the dark state to the white state, and in correspondence to this, the liquid crystal display device  40  of  FIG. 7  is driven by setting the drive voltage V 1  for the interval T 1  to 0V, the drive voltage V 2  for the interval T 2  to ±2.5V, and the overdrive voltage V 0  to +3.1V. In the example of  FIG. 13 , the display is returned again to the dark state after continuing twelve frames during the interval T 2 . 
     Referring to  FIG. 13 , the transmittance is changed already to the white state in the first frame of the interval T 2  by conducting such overdriving and that there is observed no problem of swinging of the transmittance explained with  FIG. 6 . 
       FIG. 14  shows the construction of the drive circuit  70  for conducting such overdriving. 
     Referring to  FIG. 14 , the drive circuit  70  includes: a display drive data generator  712  supplied with incident image data together with a data clock signal DCLK, a vertical synchronization signal Vsyn, a horizontal synchronizing signal Hsyn and producing display drive data therefrom; a timing controller  718  supplied with the display drive data and forming a gate control signal, display drive data and a source control signal; a gate driver  716  supplied with the gate control signal and producing an analog scanning signal, the gate driver  716  supplying the analog scanning signal to the scanning electrodes  53  of the liquid crystal display panel  50 ; and a source driver  718  supplied with the display drive data and the source control signal and producing an analog video signal, the source driver  718  further supplying the analog video signal thus produced to the data electrodes  52  of the liquid crystal display panel  50 . 
     To the display drive data generator  712 , it should be noted that a frame memory  720  formed of a ROM and holding the input image data of the previous frame, a conversion table holding the values of the coefficient A for various combinations of the voltage V 1  and the voltage V 2  and a temperature sensor  724  cooperate. 
     Thus, the display drive data generator  712  holds the incident image data of the previous frame in the foregoing frame memory  720  upon incoming of the image data of the current frame and seeks through the conversion table  723  for the corresponding coefficient A while using the current image data, the incident image data of the previous frame held in the frame memory  720  and the temperature data obtained by the temperature sensor  724  for the parameters. Further, the display drive data generator  712  multiplies the coefficient A thus discovered to the incident image data of the current frame and produces the display drive data. 
     Thus, with the present embodiment, a nearly ideal transition of transmittance such as the one shown in  FIG. 13  is realized, by restricting the tilting direction of the liquid crystal molecules  51 L by the polymer layers  55   a  and  57   a  and by applying the overdriving technology to such a liquid crystal display device. 
     Meanwhile, it should be noted that, with the liquid crystal display device of the present invention, the image of one frame is displayed over the entire screen area for the duration of full one frame interval, and hence over the full duration of 16.7 ms, in the case of displaying motion picture images with such a liquid crystal display device. Thereby, because of the visual sensory characteristics of human eyes, the changing images tend to cause the impression that different images are superimposed and blurred. 
     Thus, with the present embodiment, the backlight unit  60  disposed behind the liquid crystal display panel  50  shown in  FIG. 7  is divided into plural subunits (i)-(iv) as shown in  FIG. 15A  and carry out a quasi-vertical scanning shown in  FIG. 15B , by carrying out the activation of the subunits sequentially one by one. 
     More specifically, the backlight unit  60  includes four backlight sources  61 A- 61 D disposed behind the liquid crystal display panel  50  at the right hand side part thereof and the left hand side part thereof, wherein the backlight sources  61 A- 61 D includes respective light guide plates  60 A- 60 D, and the light guide plate  60 C, which is coupled with the optical source  61 C, is provided with an optical scatter plate  60   c  in correspondence to the region (i). 
     Similarly, the light guide plate  60 A coupled with the optical source  61 A includes an optical scatter plate  60   a  in correspondence to the foregoing region (ii), while the light guide plate  60 B coupled with the optical source  61 B includes an optical scatter plate  60   b  in correspondence to the region (iii). Further, the light guide plate  60 D coupled with the optical source  60 D is formed with an optical scatter plate  60   d  in correspondence to the foregoing region (iv). 
     Thus, when the optical source  61 C is activated, backlight emission is caused in the region (i) corresponding to the optical scatter plate  60   c , while when the optical source  61 A is activated, the backlight emission is caused in the region (ii) corresponding to the optical scatter plate  60   a.    
     Similarly, when the optical source  61 B is activated, the backlight emission is caused in the region (iii) corresponding to the optical scatter plate  60   b , while when the optical source  61 D is activated, the backlight emission is caused in the region (iv) corresponding to the optical scatter plate  60   d.    
     Thus, as shown in  FIG. 15B , the present embodiment achieves the activation of the optical sources  61 C,  61 A,  61 B and  61 D consecutively, and with this, the regions (i), (ii), (iii) and (iv) are scanned consecutively. 
     Thus, with the present embodiment, the display screen is scanned vertically within the interval of one frame by consecutively turning on and off the optical sources  61 A- 61 C of the backlight unit  60 , and the blur of the motion picture, originating from the human sensory nature, is effectively suppressed when such a backlight unit  60  is used with the construction explained before. 
     As noted previously, such quasi vertical scanning of the display screen by the backlight unit has caused further degradation of displayed image quality with the conventional MVA liquid crystal display device, and it has been not possible with such a conventional MVA liquid crystal display device to use the quasi vertical scanning of the display screen. 
     With the present invention, on the other hand, it is possible to suppress the blur of motion picture images originating from the human visual sensory nature, by combining the quasi vertical scanning achieved by on and off control of the backlight unit, and a high quality motion picture representation is achieved. 
     Second Embodiment 
       FIG. 16  shows the construction of a pixel electrode according to a second embodiment of the present invention used in the construction of  FIG. 9B  in place of the pixel electrode  54 . In  FIG. 16 , those parts explained previously are designated by the same reference numerals and the description thereof will be omitted. 
     In the embodiment of  FIG. 16 , it will be noted that the pixel electrode  64  is formed with a large number of minute cutout patterns  64 A, and thus, the liquid crystal molecules  51 L in the liquid crystal layer  51  are tilted in the elongating direction of the cutout patterns  64 A in the event a drive voltage is applied to the electrode  64 , due to the action of the localized electric field formed between adjacent electrode fingers across the cutout pattern  64 A. 
     In the illustrated example, the pixel electrode  64  includes four regions A-D characterized by respective, mutually different directions for the extending direction of the cutout patterns  64 A. 
     Further, it will be noted that the present embodiment eliminates the projecting patterns  56 A formed on the substrate  51 B with the previous embodiment. 
     Thus, the present invention is also effective with the liquid crystal display device that uses such a pixel electrode  64 . 
     Other features of the present are similar to those of the previous embodiments, and further description thereof will be omitted. 
     Third Embodiment 
       FIGS. 17A and 17B  are diagrams showing the construction of a pixel used with a liquid crystal display device  80  according to a third embodiment of the present invention, wherein those parts explained previously are designated by the same reference numerals and the description thereof will be omitted. 
     Referring to  FIG. 17A , the present embodiment uses two ITO pixel electrodes  84 A and  84 B in a single pixel region, wherein each of the pixel electrodes  84 A and  84 B is formed with the cutout patterns corresponding to the cutout patterns  54 A of  FIG. 10  explained previously. Further, a structure similar to the projecting pattern  56 A is shown on the substrate  51 B, although illustration thereof is omitted. 
     In the present embodiment, the pixel electrode  84 B is connected to an interconnection pattern  81  extending from the TFT  51 T via a via-contact  84   b  and is driven directly by the TFT  51 T, while the pixel electrode  84 A is driven via the capacitance formed between the interconnection pattern  81  and the electrode pattern  84 A as shown in  FIG. 17B . Thus, the pixel electrode  84 A is a floating electrode. 
     Referring to  FIG. 17B , the interconnection pattern  81  is formed on an interlayer insulation film covering the scanning electrode pattern  52  formed on the glass substrate  51 A and is covered by an interlayer insulation film  83  carrying the source and drain electrodes of the TFT  51 T. Further, the interlayer insulation film  83  is covered by another interlayer insulation film that carries thereon the pixel electrode  84 . 
     According to the construction of the present embodiment, the pixel electrode  84 A is coupled with the TFT  51 T via the capacitance, and thus, the threshold characteristics for the pixel electrode  84 A is different over the threshold characteristic for the case the pixel electrode  84 B is driven by the TFT  51 T, and the pixel electrode  84 A becomes active with some delay over the pixel electrode  84 B. 
     Thus, with the present embodiment, it becomes possible to realize excellent color representation over wide viewing angle by providing the pixel electrodes  84 A and  84 B with different threshold characteristics and with different area ratio. 
     Fourth Embodiment 
       FIG. 18  shows the construction of a television receiver set  90  according to a fourth embodiment of the present invention that uses the liquid crystal display device of the present invention. 
     Referring to  FIG. 18 , the television receiver set  90  includes: an RF amplifier connected to an antenna  90 A and amplifying an RF signal such as the radio signal that contains the image signals; a tuner unit  42  converting a desired channel of the RF signal to form an IF signal by frequency conversion; an IF amplifier  93  amplifying the IF signal formed by the tuner unit  42  and eliminating other frequency signals; and a detection unit  94  detecting the IF signal amplified by the IF amplifier  93  and producing image data, wherein the detection unit  94  is connected to the driver circuit  70  that drives the liquid crystal display panel  50  with the image data. 
     With the television receiver set  90  of such a construction, it becomes possible to display motion picture images based on the image signal supplied to the antenna  90 A with high contrast ratio and with high viewing angle, without causing the problem of swinging of the transmittance. Thereby, it should be noted that the liquid crystal display device  40  is not limited to the one explained with reference to  FIG. 7  but it is also possible to use the liquid crystal display devices explained with reference to other embodiments. 
     According to the present embodiment, it becomes possible to achieve representation of high quality motion pictures not only with the television receiver sets of large screen but also with compact radio set such as cellular phones. 
     Further, the present invention is not limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.