Abstract:
A wide viewing angle liquid crystal display (LCD) panel comprising an upper substrate, a lower substrate, and a liquid crystal (LC) layer is provided. The upper substrate is assembled above the lower substrate. The LC layer is interposed between the two substrates. The LC layer has LC molecules mixed with a predetermined percentage of negative anisotropic monomers. The optical axes of the monomers and the LC molecules as the LCD panel in dark state forms an angle less than 10 degree.

Description:
[0001]     This application claims the benefit of Taiwan application Serial No. 094105580, filed Feb. 24, 2005.  
       BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     This invention relates to a liquid crystal display (LCD) panel, and more particularly to a wide viewing angle LCD panel.  
         [0004]     (2) Description of the Related Art  
         [0005]     Attending with the improvement of thin film transistor (TFT) fabrication technology, LCD with the advantages of slim size, low power consumption, and low radiation emission, has become popular among various electronic devices, such as personal digital assistants (PDA), notebooks (NB), digital cameras (DC), digital videos (DV), cell phone, etc. However, the viewing angle of LCD at present is usually limited due to the optical behavior of liquid crystal (LC) layer with respect to light beams at various tilt angles.  
         [0006]     Implementations for improving viewing angle of LCD are taught in some patents, see, e.g., American patent, U.S. Pat. No. 5,410,422, “GRAY SCALE LIQUID CRYSTAL DISPLAY HAVING A WIDE VIEWING ANGLE”.  FIG. 1  describes the method taught in the patent, to interpose a birefringence compensator  110  between two linear polarizers  112 , 114 . Light beam traveling through the LC layer  116  with a large tilt angle is usually engaged with phase retardation different from the light beam traveling normal to the LCD panel. The disclosed birefringence compensator  110  characterized with a negative phase retardation to compensate the phase retardation difference so as to increase viewing angle.  
         [0007]     It is understood that the birefringence compensator  110  can be adapted to various LC molecule types, e.g., vertical aligned (VA) LC molecules, twisted nematic (TN) LC molecules, in-plane switch (IPS) LC molecules, etc. by properly compensating the phase retardation difference. However, the birefringence compensator  110  increases the thickness and the weight of the LCD panel, which leads to an important issue of increasing viewing angle without the benefit of birefringence compensator.  
       SUMMARY OF THE INVENTION  
       [0008]     A wide viewing angle LCD panel comprising an upper substrate, a lower substrate, and an LC layer, is provided in the present invention. The lower substrate is disposed below the upper substrate. The LC layer is interposed between the two substrates. LC molecules within the LC layer are mixed with a predetermined proportion of anisotropic monomers. The angle between the directions of the optical axes of the anisotropic monomers and the LC molecules as the LCD panel in a dark state is less than 10 degree.  
         [0009]     In an embodiment of the present invention, at least part of the monomers are polymerized to form a polymer network. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which:  
         [0011]      FIG. 1  is a schematic view depicting a traditional LCD panel;  
         [0012]      FIG. 2  is a cross section view depicting a first preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention;  
         [0013]      FIG. 2A  is a schematic view depicting a positive anisotropic LC molecule and a negative anisotropic monomer used in the present invention;  
         [0014]      FIG. 3  is a cross section view depicting a second preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention;  
         [0015]      FIG. 4  is a cross section view depicting a third preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention;  
         [0016]      FIG. 5  is a top view depicting a first preferred embodiment of the layout of polymer network in a pixel device of the wide viewing angle LCD panel in accordance with the present invention;  
         [0017]      FIG. 6  is a top view depicting a second preferred embodiment of the layout of polymer network in a pixel device of the wide viewing angle LCD panel in accordance with the present invention;  
         [0018]      FIG. 7  is a top view depicting a third preferred embodiment of the layout of polymer network in a pixel device of the wide viewing angle LCD panel in accordance with the present invention; and  
         [0019]      FIG. 8  is a schematic view depicting a fourth preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     As described in the related art of  FIG. 1 , the birefringence compensator  110  shows an opposite retardation characteristic with respect to the LC layer  116 , so as to compensate the phase retardation deviation for light beams with large tilt angles. By compensating the retardation deviation, the light leakage event can be prevented and the viewing angle can be increased.  
         [0021]      FIG. 2  shows a first preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention. The LCD panel has an upper substrate  210 , a lower substrate  220 , and an LC layer  240 . The lower substrate  220  is disposed below the upper substrate  210 . A lower polarizer  222  is formed on a lower surface of the lower substrate  220 . An upper polarizer  212  is formed on an upper surface of the upper substrate  210 .  
         [0022]     The LC layer  240  is interposed between the upper substrate  210  and the lower substrate  220 , and it is composed of LC molecules  242  mixed with a predetermined proportion of optical anisotropic monomers  262  uniformly distributed in the LC layer  240 . The LC molecules  242  are vertical aligned (VA) negative-type LC molecules. It is understood that the negative type LC molecules  242  has a tendency to change their optical axes a 1  in a direction perpendicular to the applied electrical field. In addition, as shown, when the LCD panel is in a dark state, the angle between the directions of the optical axes a 1 ,a 2  of the monomers  262  and the LC molecules  242  respectively is less than 10 degree, or even pointing toward the same direction.  
         [0023]     Referring to  FIG. 2A , in the LCD panel of the present embodiment, the LC molecules  242  are positive optical anisotropic (the ordinary refractive rate n o  greater than the extraordinary refractive rate n e ) and the monomers are negative optical anisotropic (n o  less than n e ). In contrast, as the LC molecules of negative optical anisotropic (n o  less than n e ) are adapted in the present embodiment, only the monomers of positive optical anisotropic (n o  greater than n e ) can be used.  
         [0024]     As described above, as the LCD panel is in the dark state, the optical axes of the negative-type LC molecules  242  biases toward the direction perpendicular to the applied electric field, which is parallel to the upper substrate  210  or the lower substrate  220 . For a light beam L 1  traveling normal to the LCD panel, the LC molecules  242  and the monomers  262  have the optical axes in directions substantially the same as the light beam L 1 . Thus, the light beam L 1  shows no retardation after passing through the LC layer  240 . Since the upper polarizer  212  has an absorption axis perpendicular to that of the lower polarizer  222 , the light beam L 1  passing through the lower polarizer  222 , the lower substrate  220 , the LC layer  240  (including the LC molecules  242  and the monomers  262 ), and the upper substrate  210  in a serial, but totally shielded by the upper polarizer  212 .  
         [0025]     For a light beam L 2  traveling with a tilt angle, the optical axes of the LC molecules  242  and the monomers  262  are in directions different from the light beam L 2 . Thus, the light beam L 2  must be engaged with some phase retardation from the LC molecules  242  and the monomers  262  respectively after passing through the LC layer  240 . As described above, the LC molecules  242  and the monomers  262  are positive and negative optical anisotropic, respectively. The light beam L 2  accesses opposite retardation events from the molecules  242  and the monomers  262 . Thus, the unwanted retardation deviation from the LC molecules  242  can be compensated by the monomers  262  to prevent the light beam L 2  passing through the upper polarizer  212  from light leakage.  
         [0026]      FIG. 3  shows a second preferred embodiment of a wide viewing angle LCD panel in accordance with the present invention. The LCD panel has an upper substrate  210 , a lower substrate  220 , an LC layer  240 , and a polymer network  260 . The lower substrate  220  is disposed under the upper substrate  210 . A lower polarizer  222  is formed on a lower surface of the lower substrate  220 . A upper polarizer  212  is formed on an upper surface of the upper substrate  210 . The LC layer  240  is interposed between the two substrates  210  and  220 .  
         [0027]     In the present embodiment, the LC molecules  242  within the LC layer  240  are VA negative-type LC molecules. The polymer network  260  is composed of polymerized optical anisotropic monomers  262  and shows a wall-like structure extended from an upper surface of the lower substrate  220  toward the upper substrate  210 . There may be a gap formed between the polymer network  260  and the upper substrate  210 . The polymerization of the polymer network  260  restricts the orientation of the monomers  262  to guarantee the angle between the optical axes of the monomers  262  and the LC molecules  242  in the dark state less than 10 degree.  
         [0028]     Referring to  FIG. 3 , in the LCD panel of the present embodiment, the LC molecules  242  are positive optical anisotropic (n o  is greater than n e ) and the monomers are negative optical anisotropic (n o  is less than n e ). As shown, when the LCD panel is in the dark state, the optical axes of the LC molecules  242  within the LC layer  240  are in directions perpendicular to the upper substrate  210  or the lower substrate  220 . Thus, it is understood that the optical axes of the monomers  262  are also substantially perpendicular to the upper substrate  210  or the lower substrate  220 . For the light beam L 1  traveling normal to the LCD panel, the optical axes of the LC molecules  242  and the monomers  262  are substantially in directions the same as the light beam L 1 . Thus, the light beam L 1  shows no retardation after passing through the LC layer  240  and the polymer network  260 . Since the upper polarizer  212  has the absorption axis perpendicular to that of the lower polarizer  222 , the light beam L 1  passing through the lower polarizer  222  would be totally shielded by the upper polarizer  212 .  
         [0029]     For the light beam L 2  traveling with a tilt angle, the optical axes of the LC molecules  242  and the monomers  262  are in directions different from the light beam L 2 . Thus, the light beam L 2  must be engaged with some phase retardation from the LC molecules  242  and the monomers  262  in the polymer network  260 , respectively, after passing through the LC layer  240 . As described above, the LC molecules  242  are positive optical anisotropic. The monomers  262  of negative optical anisotropic are polymerized to maintain in directions perpendicular to the upper substrate  210  or the lower substrate  220 . The light beam L 2  accesses opposite retardation events from the LC molecules  242  and the monomers  262  respectively. Thus, the unwanted retardation deviation of the LC molecules  242  is compensated by the monomers  262  to prevent the light beam L 2  passing through the upper polarizer  212  from light leakage.  
         [0030]     In order to make sure the light beam L 2  accessing enough opposite phase retardation from the monomers  262 , the wall-like structure of the polymer network  260  may be extended from the upper surface of the lower substrate  220  toward the upper substrate  210 , or the wall-like structure of the polymer network  260  should be at least extend from the lower substrate  220  upward or from the upper substrate  210  downward with a gap formed between the upper substrate  210  or the lower substrate  220  and the polymer network  260  smaller than half the thickness of the LC layer  240 .  
         [0031]      FIG. 4  shows a third preferred embodiment of the wide viewing angle LCD panel in accordance with the present invention. In contrast with the first embodiment of  FIG. 2 , the present embodiment uses horizontal aligned LC molecules, such as in-plane switch (IPS) LC molecules, instead. It should be noted that the optical axes of the monomers  264  within the polymer network  260  are parallel to the upper substrate  210  or the lower substrate  220 , and an angle formed between the axes of the LC molecules  244  and the monomers  264  is less than 10 degree. For IPS LC molecules, the optical axes of the monomers  264  are substantially parallel to the upper substrate  210  or the lower substrate  220  where the monomers  264  are negative optical anisotropic. The optical axes of the monomers  264  are substantially perpendicular to the upper substrate  210  or the lower  220  substrate, or substantially parallel to the upper substrate  210  or the lower substrate  220  but perpendicular to the optical axes of LC molecules  244  where the monomers  264  are positive optical anisotropic.  
         [0032]     As the LCD panel is in the dark state, the optical axes of the LC molecules  244  in the LC layer  240  are parallel to the upper substrate  210  or the lower substrate  220  and perpendicular to the absorption axis of the lower polarizer  222 . Since the light beam L 1  shows linearly polarization in a direction perpendicular to absorption axis of the lower polarizer  222  entering the LC layer  240 , the polarization direction of the light beam L 1  and the optical axes of the LC molecules  244  are substantially pointing to the same direction. In addition, the optical axes of the monomers  264  and the LC molecules  244  are substantially pointing to the same direction. Thus, the light beam L 1  accesses no retardation from the LC molecules  244  and the monomers  264 . Since the absorption axis of the upper polarizer  212  is perpendicular to that of the lower polarizer  222 , the light beam L 1  passing through the lower polarizer  222  would be totally shielded by the upper polarizer  212 .  
         [0033]     For the light beam L 2  traveling with a tilt angle, there are angles formed between the linearly polarization direction of the light beam L 2  and the optical axes of the LC molecules  244  and the monomers  264 , respectively. Thus, the light beam L 2  must access retardation events from the LC molecules  244  and the monomers  264  within the polymer network  260  after passing through the LC layer  240 . As described above, since the LC molecules  244  and the monomers  264  are positive and negative optical anisotropic respectively, the light beam L 2  must access opposite retardation from the LC molecules  244  and the monomers  264 . The unwanted retardation deviation from the LC molecules  244  can be compensated by the contribution of the monomers  264  so as to prevent the light beam L 2  passing through the upper polarizer  212  from light leakage.  
         [0034]     Although the above mentioned embodiments only describes the cases with VA type LC molecules  242  and IPS type LC molecules  244 , typical twisted nematic (TN) type LC molecules can be applied in the present invention, just under the limitation that the angle between the optical axes of the anisotropic monomers and TN type LC molecules as the LCD panel in the dark state less than 10 degree.  
         [0035]      FIG. 5  shows a top view of a first preferred embodiment of the polymer network layout within a pixel device in accordance with the present invention. As shown, the polymer network  260  is a quadrilateral network distributed in the LC layer  240  to make sure the light beams with large tilt angles traveling along various directions may access opposite phase retardation from the LC molecules and the monomers in the polymer network  260 .  
         [0036]      FIG. 6  shows a top view of a second preferred embodiment of the polymer network layout within a pixel device in accordance with the present invention. As shown, the polymer network  260  is a hexagonal network  260  distributed in the LC layer  240  to make sure that the light beams with large tilt angles traveling along various directions may access opposite phase retardation from the LC molecules and the monomers in the polymer network  260 .  
         [0037]      FIG. 7  shows a top view of a third preferred embodiment of the polymer network layout within a pixel device in accordance with the present invention. As shown, the polymer network in the pixel device has two parts extended from a middle of an edge to both ends of an opposite edge to make sure that the light beams with large tilt angles traveling along various directions access opposite retardation from the LC molecules and the monomers in the polymer network  260 .  
         [0038]     As mentioned above, the polymer network  260  adapted in the present invention restricts the orientation of the monomers  262 ,  264  so as to achieve the object of compensating the retardation deviations of light beam L 2  passing through the LC molecules  242 ,  244  to increase the viewing angle of the LCD panel. Therefore, the compensator  110  described in related art can be omitted to reduce the fabrication cost, the weight, and the thickness of the LCD panel. In addition, for a concern of better compensation ability, in the fourth preferred embodiment of the LCD panel in accordance with the present invention as shown in  FIG. 8 , the compensator  110 , such as an a-plate or a biaxial film, may be interposed between the lower substrate  220  and the lower polarizer  222  or the upper substrate  210  and the upper polarizer  212  (not shown) to further prevent the light leakage event of the LCD panel in the dark state.  
         [0039]     While the embodiments of the present invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the present invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the present invention.