Abstract:
A driving method for activating an optical self-compensated birefringence mode liquid crystal device is provided. The optical self-compensated birefringence mode liquid crystal device has plural pixel structures, plural substrates and a liquid crystal layer sandwiched between the plural substrates. Each of said plural pixel structures comprises a first electrode, a second electrode, a pixel electrode and a common electrode. The driving method comprising steps of: providing a space between said first electrode and said second electrode on one of plural substrate; providing a first potential difference between said first electrode and said second electrode to generate a first electric field; and performing an initialization process from a bend of said second electrode to transitioning an alignment state of said liquid crystal layer from a non-display alignment state to a display alignment state by said first electric field. Further, generate a second electric field by a second potential difference between said pixel electrode and said common electrode.

Description:
FIELD OF THE INVENTION 
   The present application relates to a pixel structure and a driving method for a liquid crystal device, and more particularly to the pixel structure and the driving method for the optically compensated birefringence (OCB) mode liquid crystal device. 
   BACKGROUND OF THE INVENTION 
   In recent years, studies on the optically compensated birefringence (OCB) cell that is to be used as a liquid crystal cell instead of a twisted nematic (TN) cell have been quickly increased. In the OCB mode liquid crystal device, the liquid crystal molecules therein are in splay state at the initial state. However, when a voltage is applied to the OCB mode liquid crystal device, the liquid crystal molecules therein will transit from the splay state to the bend state, and it is required to spend some time for the transition from the splay state to the bend state. In the bend state, the top and bottom liquid crystal molecules are always oriented symmetrically, and thus to compensate the birefringence of liquid crystal molecules so as to obtain the uniform viewing angle characteristic at all directions is more easily than that obtained with the orientation division method, and a high-speed response characteristic that is one order faster than that for the conventional TN cells may also be obtained accordingly. 
     FIGS. 1A and 1B  respectively illustrate the liquid crystal molecules in splay state and bend state in the OCB mode liquid crystal display device. As shown in  FIG. 1A , in splay state, the liquid crystal molecules  104  are uniformly splayed between the glass substrates  100  and  102 . However, when a voltage is applied to the glass substrates  100  and  102 , the liquid crystal molecules  104  will be in bend state, as shown in  FIG. 1B . In which, the transition time of the liquid crystal molecules  104  from the splay state to the bend state is one of the determinants for the OCB mode liquid crystal display device due to the fact that all the electro-optical properties of the OCB mode liquid crystal display device are operated when the liquid crystal molecules therein are in bend state. 
   However, some pixel structures have been disclosed, such as those disclosed in U.S. Pat. Nos. 6,115,087, 6,226,058, 6,661,491 and U.S. Pat. No. 6,597,424, but, some of them are not suitable for OCB mode liquid crystal display devices and there still exist some demerits in the disclosed pixel structures. In addition, the conventional pixel structures usually have the demerits, for example, a space exists between the pixel electrode and the gate electrode, and the common electrode must be introduced and overlapped with the pixel electrode for a certain area so as to form a storage capacitor. However, the above two demerits will result in a small aperture and cause the conventional pixel structures incompatible with the three-level gate driving. 
   In addition, although some driving methods for a liquid crystal device have been disclosed, such as that Takayuki Konno et al., (U.S. Pat. No. 6,873,377) and Katsuji Hattori et al., (U.S. Pat. No. 6,671,009) have disclosed a driving method for an OCB mode liquid crystal display and Hajime Nakamura et al., (U.S. Pat. No. 6,005,646) have disclosed another driving method for a thin film transistor liquid crystal display (TFT/LCD), there still exist some defects in the disclosed driving methods. For example, the driving method proposed by Katsuji Hattori et al. has a complicated signal input procedure and the applied system design always needs an alignment transition driving circuit, a switching control circuit and a switching circuit. In other words, the cost for the driving method of Katsuji Hattori et al. is always high and the relevant driving method is not so practical, especially for the trend of compactness. In addition, since the potential difference between the signal electrode and the common electrode is morn than 10 volts and that between the gate electrode and the signal electrode is also more than 10 volts in the driving method proposed by Hajime Nakamura, there might exist some problems about the poor uniformity and the slow transition time in driving method of the prior arts. 
   As above, since all the electro-optical properties of the OCB mode liquid crystal display device are operated only when the liquid crystal molecules therein are in bend state, the liquid crystal molecules in the OCB mode liquid crystal display devices need to be transformed from the splay state (non-display state) into the bend state (display state) before being used and there still exist some demerits in the conventional pixel structures and driving methods, new driving methods with shorter transition time and new pixel structures contributive to shorten the transition time for activating OCB mode liquid crystal display device are desired. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present application, a driving method for activating an optical self-compensated birefringence mode liquid crystal device is provided. The optical self-compensated birefringence mode liquid crystal device has plural pixel structures, plural substrates and a liquid crystal layer sandwiched between the plural substrates. Each of said plural pixel structures comprises a first electrode, a second electrode, a pixel electrode. The driving method comprising steps of: providing a space between said first electrode and said second electrode on one of plural substrate; providing a first potential difference between said first electrode and said second electrode to generate a first electric field; and performing an initialization process from a bend of said second electrode to transitioning an alignment state of said liquid crystal layer from a non-display alignment state to a display alignment state by said first electric field. Further, generate a second electric field by a second potential difference between said pixel electrode and a common electrode. 
   In accordance with another aspect of the present application, a liquid crystal display device is provided. The liquid crystal display device has a first substrate, a second substrate opposite to the first substrate, a pixel electrode formed on the first substrate, and a liquid crystal layer sandwiched between the first substrate and the second substrate. The liquid crystal display device includes a first electrode provided on the first substrate, a second electrode located on the first substrate and having a bend portion, and a driving means generating a potential difference between the first electrode and the second electrode. There is a space between the first electrode and the second electrode. 
   The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein: 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIGS. 1A and 1B  respectively illustrate the liquid crystal molecules in splay state and bend status in the OCB mode liquid crystal display device; 
       FIGS. 2A and 2B  respectively show the electrode structure of the pixel structure according to a first preferred embodiment of the present application and the cross-sectional view along the AA′ line in  FIG. 2A ; 
       FIGS. 2C and 2D  respectively show the diagrams of the bias electrode supplied with an alternating voltage and a direct voltage; 
       FIGS. 2E and 2F  respectively show the relative voltage relationships among the pixel electrode, the gate electrode, the bias electrode, the data line and the common electrode under the positive polarity and the negative polarity when an alternating voltage is applied to the OCB mode liquid crystal display device; 
       FIGS. 3A and 3B  respectively show a pixel structure of an optical self-compensated birefringence mode liquid crystal device according to a second and a third preferred embodiments of the present application; 
       FIGS. 4A to 4D  respectively show the pixel structures of an optical self-compensated birefringence mode liquid crystal device according to the forth, fifth, sixth and seventh preferred embodiments of the present application; 
       FIGS. 5A to 5F  respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to eighth, ninth, tenth, eleventh, twelfth and thirteenth preferred embodiments of the present application; and 
       FIGS. 6A to 6C  respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to the fourteenth, fifteenth, and sixteenth preferred embodiments of the present application. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present application will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this application are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
   Please refer to  FIGS. 2A and 2B , which respectively show the pixel structure according to a first preferred embodiment of the present application and the cross-sectional view along the AA′ line in  FIG. 2A . 
   As shown in  FIGS. 2A and 2B , the pixel electrode  202  is partially overlapped with the bias electrode  201 , the data line  203  has an extension portion  2031  with a meander shape extending to the middle of the pixel region. In addition, as shown in  FIG. 2B , a common electrode  208  is located on the upper glass substrate  205 , the pixel electrode  202  is located between the bias electrode  201  and the common electrode  208 , and the crystal liquid molecules.  206  are sandwiched between the upper glass substrate  205  and the lower glass substrate  207 . In addition, the bias electrode  201  and the gate line  204  are in the same layer. Furthermore, as shown in  FIG. 2A , there exists a space  209  between the bias electrode  201  and the extension portion  2031 . And the bias electrode  201  includes an opening for containing the extension portion  2031  of the data line  203  and the space  209 . Wherein the edges of the opening of the bias electrode  201  and the extension portion  2031  are complementary to each other; and the shape of the space  209  between the bias electrode  201  and the extension portion  2031  is the same as that of the extension portion  2031 . It should be noted that the extension portion  2031  could also be in the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape. In general, the applied space  209  is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. Besides, it should be noted that the space  209  and the opening of the bias electrode  201  are in one shape selected from a group consisting of the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape, L-shape, stair-shape, bend shape, meander-shape and so on. 
   During the process of driving an OCB mode liquid crystal display device with the pixel structure shown in  FIGS. 2A and 2B , a lateral electric field is first formed by modulating the potential difference between the bias electrode  201  and the extension portion  2031  of the data line  203  so as to result in the bend nuclei of the liquid crystal molecules therein (not shown), and then a vertical electric field is formed by modulating the potential difference between the pixel electrode  202  and the common electrode  208  so as to result in the bend transition of the liquid crystal molecules therein. When the applied voltages on the bias electrode  201 , the pixel electrode  202  and common electrode  208  are respective ±20 Volt, ±6 Volt and −30 Volt, it is found that the transition time for the liquid crystal molecules (not shown) is less than 0.5 second. In addition, when the applied voltages on the bias electrode  201 , the pixel electrode  202  and common electrode  208  are respective 25 Volt, ±6 Volt and 30 Volt, it is found the transition time for the liquid crystal molecules is similarly less than 0.5 second. However, in order to simply illustrate the applied voltages of the driving method according to the present application could be provided by an alternating voltage or a direct voltage,  FIGS. 2C and 2D , which respectively show the diagrams of the driving method activated by an alternating voltage and a direct voltage, are provided. In  FIGS. 2C , and  2 D, the voltages of the bias electrode, the data line and the common electrode are respectively indicated by Vbias, Vd and Vcom. 
   As above, however, since the given period for transforming the alignment state of the liquid crystal molecule from the splay state into the bend state at the start of LCDs operation could be substantially reduced according to the driving method and the pixel structure of the present application, the LCDs using one of the pixel structure and driving method or both of the present invention has a high-speed response as well as a high display quality. 
   Please refer to  FIGS. 2E and 2F , which respectively show the voltage relationships among the pixel electrode, the gate electrode, the bias electrode, the data line and the common electrode under the positive polarity and the negative polarity when an alternating voltage is applied to the OCB mode liquid crystal display device. In  FIGS. 2E and 2F , the voltages of the pixel electrode, the gate electrode, the bias electrode, the data line and the common electrode are respectively indicated by Vp, Vg, Vb, Vd and Vcom. After the relevant pixel structure is configured, Vp thereof will be easily coupled to a higher voltage (or a lower voltage) due to the Vb coupling effect and the potential difference ΔVpc among Vp and Vc will be increased accordingly. However, when the thin film transistor (TFT) (not shown) is turned on again, the potential difference ΔVpc will become small again. 
   Please refer to  FIGS. 3A and 3B , which respectively show a pixel structure of an optical self-compensated birefringence mode liquid crystal device according to a second and a third preferred embodiments of the present application. 
   As shown in  FIG. 3A , in the pixel structure according to the present application, the bias electrode  301  is partially overlapped with the pixel electrode  302  via the saw-toothed protrusions  3011  and  3021  respectively belong to the bias electrode  301  and pixel electrode  302 . The driving transistor  305  is electrically connected to the data line  303  and the gate line  304  and the pixel electrode  302  for controlling the potential differences there-among. Therefore, by scanning the gate line  304  in accordance with the gate signals, the driving transistors  305  in the same given gate line  304  are turned on. At the same time, signals in the data line  303  are transferred to the pixel electrode  302  through the driving transistor  305  to show a picture on the liquid crystal display device. When the applied voltages for the data line  303 , the gate line  304  and the bias electrode  301  are respectively ±6 Volt, 10 Volt and ±20 Volt, it is found that the seed propagations of the liquid crystal molecules are not only easily formed at the bottom of the pixel electrode  302 , where the pixel electrode  302  is not overlapped with the gate line  304 , but also at the top of the pixel electrode  302 , where the pixel electrode  302  is overlapped with the bias electrode  301  (the relevant result is not shown here). Furthermore, as in  FIG. 3A , a storage capacitor (not shown) is inherently formed between the pixel electrode  302  and the gate line  304 . Therefore, the aperture ratio of the new pixel structure in  FIG. 3A  is increased when it is compared to the conventional ones. Furthermore, it should be noted that, in a similar embodiment, it is possible that the data line  303  is partially overlapped with the pixel electrode  302 , as shown in  FIG. 3B . 
   Please refer to  FIGS. 4A to 4D , which respectively show the pixel structures of an optical self-compensated birefringence mode liquid crystal device according to the forth, fifth, sixth and seventh preferred embodiments of the present application. 
   As shown in  FIGS. 4A to 4D , all the pixel electrodes  402  according to the forth, fifth, sixth and seventh preferred embodiments of the present application are partially overlapped with the bias electrodes  401 . In which, the protrusions of the pixel electrode  402  and the bias electrode  401  could be taper-shape, rectangular, or saw-toothed and so on. 
   In addition, please also refer to  FIGS. 5A to 5E , which respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to eighth, ninth, tenth, eleventh, twelfth and thirteenth preferred embodiments of the present application. These embodiments introduce an initialization process activated by an lateral electric field provided from any two selected from the group consisting of the gate line, bias electrode and data line. 
   As shown in  FIG. 5A , the pixel electrode  502  is partially overlapped with the bias electrode  501 , and there is a space  509  between the bias electrode  501  and the gate line  504 . The bias electrode  501  is located in the same layer of the gate line  504 . In the other hand, the bias electrode  501  and the gate line  504  could be formed and defined simultaneously. Furthermore, as shown in  FIG. 5A , the edges of the bias electrode  501  and the gate line  504  are complementary to each other. And the shape of the space  509  between the bias electrode  501  and the gate line  504  is dependent on that of extension portion  5031 ,such as meander-shaped. 
   However, during the driving process, since there is a space  509  between the bias electrode  501  and the gate line  504 , a lateral electric field could be formed by modulating the potential difference between the bias electrode  501  and the gate line  504 . In addition, the pixel electrode  502  is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween. 
   As shown in  FIGS. 5B and 5C , the pixel electrode  502  is partially overlapped with the bias electrode  501 , and the data line  503  has a bend  5031 . Furthermore, although the data line  503  is partially overlapped with the bias electrode  501 , there still exists a space  509  between the bias electrode  501  and the bend  5031 . The bias electrode  501  includes an opening for containing the bend  5031  of the data line  503  and the space  509 . The bias electrode  501  is located in the same layer of the gate line  504 . In the other hand, the bias electrode  501  and the gate line  504  could be defined simultaneously. In addition, it should be noted that the bias electrode  501  could be within the pixel region, as shown in  FIG. 5B , or could be an extension portion of the gate line  804 , as shown in  FIG. 5C . And, the bias electrode  501  is partially overlapped with pixel electrode  802  in  FIGS. 5B and 5C . Furthermore, as shown in  Figs. 5B and 5C , the edges of the opening of the bias electrode  501  and the bend  5031  are complementary to each other, and the shape of the spaces  509  between the bias electrode  501  and the bend  5031  are dependent on that of extension portion  5031 , such as meander shaped. 
   However, during the driving process, since there is a space  509  between the bias electrode  501  and the data line  503 , a lateral electric field could be formed by modulating the potential difference therebetween. In addition, since the pixel electrode  502  is overlapped with the common electrode located on the upper glass substrate (not shown), a vertical electric field could be formed by modulating the potential difference therebetween. 
   As shown in  FIGS. 5D and 5E , the pixel electrode  502  is partially overlapped with the gate line  504 , and the data line  503  has an extension portion  5031 . Furthermore, there exists a space  509  between the gate line  504  and the extension portion  5031 . And, the gate line  504  includes an opening for containing the extension portion  5031  of the data line  503  and the space  509 . Besides, it should be noted that the extension portion  5031  could be a triangle-shaped protrusion or a meander shape including the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape. Furthermore, as shown in  FIGS. 5D and 5E , the edges of the opening of the gate line  504  and the extension portion  5031  are complementary to each other, and the shape of the space  509  between the gate line  804  and the extension portion  5031  is dependent on that of extension portion  5031 ,such as triangle-shaped or meander-shaped. 
   However, during the driving process, since there is a space  509  between the gate line  504  and the extension portion  5031  of the data line  503 , a lateral electric field could be formed by modulating the potential difference therebetween. In addition, the pixel electrode  502  is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween. 
   As shown in  FIG. 5F , the bias electrode  501  is partially overlapped with the pixel electrode  502 , and the data line  503  has the bend  5031  with a meander shape. The bias electrode  501  located in the same layer of the data line  503  has the protrusion  5011 . In the other hand, the bias electrode  501  and the date line  503  could be defined simultaneously. In addition, there exists a space  509  between the protrusion  5011  and the meander-shaped bend  5031 . Furthermore, the edges of the protrusion  5011  and the meander-shaped bend  5031  are complementary to each other. As shown in  FIG. 5F , the shape of space  509  between the protrusion  5011  and the meander-shaped bend  5031  is dependent on that of the meander-shaped bend  5031 . 
   However, during the driving process, since there is a space  509  between the bias electrode  501  and the data line  503 , a lateral electric field could be formed by modulating the potential difference therebetween. In addition, the pixel electrode  502  is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween. 
   In general, as shown in  FIGS. 5A to 5F , the applied space  509  is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. The pixel electrode  502  is made from a transparent conductor, such as ITO, IZO, ITZO or AZO, and so on. Besides, the space  509  and the opening of the bias electrode  501  and gate line  504  are in a shape selected from the group consisting of the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, cross-like shape, L-shape, stair-shape, bend shape, meander-shape and so on. 
   However, it also should be noted that, according to the present application, a lateral electric field is formed by modulating the potential differences between any two selected from the group consisting of the gate line, bias electrode and data line. Furthermore, the above-applied voltages need not be limited to the disclosed embodiments. In addition, as above, it is also found that no matter an alternating voltage or a direct voltage is supplied to the bias electrode, the transition time for the liquid crystal molecules according to the driving method of the present application is less than 0.5 sec, which is much less than the transition time of the conventional driving method. 
   In addition, please also refer to  FIGS. 6A to 6C , which respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to fourteenth, fifteenth, and sixteenth preferred embodiments of the present application. 
   As shown in  FIGS. 6A to 6C , the gate line  604  has an extension portion  6041  close to the cross point of the gate line  604 . Besides those illustrated in  FIGS. 6A to 6C , the extension portion  6041  be also able in other shapes, such as the triangle, rectangle, L shape, stair shape, bend shape, meander shape and so on. Moreover, a first bending electrode  6031  of the data line  603  and a second bending electrode  6061  are over the extension portion  6041 . And the second bending electrode  6061  is connected to the pixel electrode  602 . Furthermore, there exists a space  609  between the first bending electrode  6031  and the second bending electrode  6061 . And the shapes of the first bending electrode  6031  and the second bending electrode  6061  are complementary to each other. In other words, the first bending electrode  6031  and the second bending electrode  6061  have the similar pattern to that of the extension portion  6041  of the gate line  604 . 
   As shown in  FIGS. 6A-6C , the shape of the space  609  between the first bending electrode  6031  and the second bending electrode  6061  is the same as that of the first bending electrode  6031  and the second bending electrode  6061 . It should be noted that, besides those disclosed in  FIGS. 6A-6C , the space  609  could be in other shapes, such as the triangle, rectangle, L shape, stair shape, bend shape, meander-shape and so on. In addition, the bending points of the first bending electrode  6031  and the second bending electrode  6061  are toward the same direction to that of the data line  603  or the gate line  604 . 
   The second bending electrode  6061 , as the drain electrode of the transistor  606 , is connected to the pixel electrode  602 . Therefore, the signal in the data line  603  is ably transferred to the pixel electrode  602  via the first bending electrode  6031 , as the source electrode of the transistor  606 . However, by scanning the gate line  604  in accordance with the gate signals, the transistors  606  in the same given gate line  604  are turned on. At the same time, signals in the data line  603  are ably transferred to the pixel electrode  602  through the transistor  606  to show a picture on the relevant liquid crystal display device (not shown). 
   In general, the applied space  609  is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. The pixel electrode  602  is made from a transparent conductor, such as ITO, IZO, ITZO or AZO, and so on. Besides the above, the space  609  and the first bending electrode  6031  and the second bending electrode  6061  are also in other shapes, such as the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape, L shape, stair shape, bend shape, meander shape and so on. 
   As above, according to the pixel structure and the driving method of the present application, the period for transforming the liquid crystal molecule from the splay state into the bend state at the start-up of LCDs operation could be substantially reduced, and the LCDs using the pixel structure of the present application will have a high-speed response as well as a high display quality. 
   Furthermore, since the pixel structures of the present application are more compact than the conventional ones and have a high-speed response as well as a high display quality, and the driving methods thereof can significantly reduce the transition time of the liquid crystal molecules therein, the present application does have the progressiveness, novelty and industrial utility. 
   While the application has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the application need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present application which is defined by the appended claims.