Liquid crystal display device and driving method of the same

Abstract

The invention relates to a liquid crystal display device used for a display part of an information equipment and a driving method thereof, and has an object to provide a liquid crystal display device in which excellent viewing angle characteristics can be obtained and a driving method thereof. When a relatively high level data voltage is applied to a gate electrode of a TFT, a driving voltage is applied to a liquid crystal layer for a long time and a white display is realized. When a relatively low level data voltage is applied to the gate electrode of the TFT, the driving voltage is not applied to the liquid crystal layer, and a black display is realized. When an intermediate data voltage between the high level and the low level is applied to the gate electrode of the TFT, the TFT keeps an on state for a time determined by a time constant depending on a capacitance and a resistance. The driving voltage is applied to the liquid crystal layer for the on time. By this, a half tone display is realized according to the ratio of the on time of the TFT in one frame period.

1. A driving method of a liquid crystal display device, comprising the steps of:
 applying a data voltage from a data voltage line to a first thin film transistor in a pixel; 
 applying a driving voltage from a driving voltage line to a second thin film transistor in the pixel only in a predetermined time in one frame period; and 
 displaying a predetermined gradation to the pixel by changing an application time of the driving voltage in accordance with a magnitude of the data voltage from the first thin film transistor applied to a gate electrode of the second thin film transistor. 
 
     
     
       2. A driving method of a liquid crystal display device according to  claim 1 , wherein the driving voltage is set to a voltage or within a voltage range in which the liquid crystal can perform a high speed response. 
     
     
       3. A driving method of a liquid crystal display device according to  claim 1 , wherein the liquid crystal is aligned almost vertically to or parallel to a substrate surface at a time when the driving voltage is applied or at a time when the driving voltage is not applied. 
     
     
       4. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other; 
 a liquid crystal sealed between the pair of substrates; 
 a gate bus line formed on one of the substrates; 
 a data bus line formed to intersect the gate bus line through an insulating film, to which a predetermined gradation voltage is applied; 
 a first thin film transistor formed in a vicinity of an intersection position of the gate bus line and the data bus line; 
 a second thin film transistor, a gate electrode of which is connected to a source electrode of the first thin film transistor; 
 a pixel electrode connected to a source electrode of the second thin film transistor; 
 a driving voltage bus line which is connected to a drain electrode of the second thin film transistor and to which a driving voltage to drive the liquid crystal is applied; and 
 a first capacitance and a first resistance connected in parallel with each other at a side of the source electrode of the first thin film transistor. 
 
     
     
       5. A liquid crystal display device according to  claim 4 , further comprising a second capacitance and a second resistance connected in parallel with each other at a side of the source electrode of the second thin film transistor. 
     
     
       6. A liquid crystal display device according to  claim 5 , wherein the second capacitance is a liquid crystal capacitance. 
     
     
       7. A liquid crystal display device according to  claim 4 , wherein the pair of substrates respectively include vertical alignment films on opposite surfaces, and the liquid crystal has a negative dielectric anisotropy. 
     
     
       8. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other; 
 a liquid crystal sealed between the pair of substrates; and 
 pixels disposed in a matrix form and including a plurality of aligned regions, each of the aligned regions further having a plurality of sub-regions where pre-tilt angles of the liquid crystal are different from each other, wherein the liquid crystal includes a photo-cured material which is obtained by curing a photo-curing composition, and 
 the pre-tilt angle of at least one of the sub-regions is regulated by the photo-cured material. 
 
     
     
       9. A liquid crystal display device according to  claim 8 , wherein the pre-tilt angle of at least one of the sub-regions is about 90°. 
     
     
       10. A liquid crystal display device according to  claim 8 , wherein the pre-tilt angle of all sub-regions is 80° or more. 
     
     
       11. A liquid crystal display device according to  claim 8 , wherein the plurality of aligned regions are substantially equally divided. 
     
     
       12. A liquid crystal display device according to  claim 8 , wherein the pre-tilt angle of at least a first one of the sub-regions is regulated by the photo-cured material cured in the first sub-region with a voltage applied to the liquid crystal, and the pre-tilt angle of at least a second one of the sub-regions is regulated by the photo-cured material cured in the second sub-region while no voltage is applied to the liquid crystal. 
     
     
       13. A liquid crystal display device according to  claim 8 , wherein the pair of substrates respectively include vertical alignment films on opposite surfaces, and the liquid crystal has a negative dielectric anisotropy. 
     
     
       14. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other; 
 a liquid crystal sealed between the pair of substrates; 
 a plurality of pixel regions disposed in a matrix form; and 
 a pixel electrode formed in each of the pixel regions, including a plurality of stripe electrodes and spaces between the stripe electrodes, some of the plurality of stripe electrodes and spaces being formed to have different widths from each other. 
 
     
     
       15. A liquid crystal display device according to  claim 14 , wherein the liquid crystal includes a photo-cured material which is obtained by curing a photo-curing composition, and
 a pre-tilt angle is regulated by the photo-cured material. 
 
     
     
       16. A liquid crystal display device according to  claim 14 , wherein the pair of substrates respectively include vertical alignment films on opposite surfaces, and
 the liquid crystal has a negative dielectric anisotropy. 
 
     
     
       17. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other;   a liquid crystal sealed between the pair of substrates;   a plurality of pixel regions disposed in a matrix form;   a pixel electrode formed in at least one pixel region, the pixel electrode including at least a connection electrode, a plurality of stripe electrodes connected to the connection electrode, and   a plurality of spaces between the stripe electrodes, at least one of the plurality of spaces being formed to have a different width than other spaces,   the connection electrode including a first connection electrode formed in the center of the pixel region.   
     
     
       18. A liquid crystal display device according to claim 17, the liquid crystal comprising a photo-cured material regulating a pre-tilt angle of the liquid crystal. 
     
     
       19. A liquid crystal display device according to claim 18, wherein the photo-cured material is obtained by curing a photo-curing compound. 
     
     
       20. A liquid crystal display device according to claim 17, wherein the pair of substrates respectively include vertical alignment films on opposite surfaces, and the liquid crystal has a negative dielectric anisotropy. 
     
     
       21. A liquid crystal display device according to claim 17, wherein the stripe electrodes are the same width. 
     
     
       22. A liquid crystal display device according to claim 17, wherein the stripe electrodes and spaces are arranged symmetrically with respect to the first connection electrode. 
     
     
       23. A liquid crystal display device according to claim 17, wherein adjacent stripe electrodes are parallel to each other. 
     
     
       24. A liquid crystal display device according to claim 17,
 wherein the connection electrode includes a second connection electrode formed perpendicular to the first connection electrode, and the first and the second connection electrodes define four domains within the pixel region.   
     
     
       25. A liquid crystal display device according to claim 17, comprising:
 a bus line for providing a signal to at least one of the stripe electrodes,   wherein the stripe electrode is connected to the first connection electrode, the first connection electrode being formed parallel to the bus line.   
     
     
       26. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other;   a liquid crystal sealed between the pair of substrates;   a plurality of pixel regions disposed in a matrix form;   a pixel electrode formed in at least one pixel region, the pixel electrode including at least a connection electrode and a plurality of stripe electrodes connected to the connection electrode, and   a plurality of spaces between the stripe electrodes, at least one of the plurality of stripe electrodes being formed to have a different width than other stripe electrodes,   the connection electrode including a first connection electrode formed in the center of the pixel region.   
     
     
       27. A liquid crystal display device according to claim 26, comprising a photo-cured material regulating a pre-tilt angle of the liquid crystal. 
     
     
       28. A liquid crystal display device according to claim 27, wherein the photo-cured material is obtained by curing a photo-curing compound. 
     
     
       29. A liquid crystal display device comprising:
 a pair of substrates disposed to be opposite to each other;   a liquid crystal sealed between the pair of substrates;   a plurality of pixel regions disposed in a matrix form;   a plurality of stripe electrodes formed in the pixel regions, the stripe electrodes being placed adjacent to and connected to each other;   a plurality of spaces formed between the stripe electrodes;   a photo-cured material regulating an alignment of the liquid crystal,   wherein at least one of the pixel regions includes a first pixel region and a second pixel region, and   at least one of (a) some of the stripe electrodes and (b) some of the spaces in the first pixel region are different in width from at least one of (c) some of the stripe electrodes and (d) some of the spaces in the second pixel region.   
     
     
       30. A liquid crystal display device according to claim 29, comprising:
 a bus line for providing a signal to at least one of the stripe electrodes,   wherein the stripe electrode is connected to the first connection electrode, the first connection electrode being formed parallel to the bus line.