Liquid crystal display device and associated fabrication method

Abstract

In a liquid crystal display device which displays images by changing light transmission through formation of a bend alignment state of the liquid crystal, a large pretilt angle domain is formed on at least either the surface of the pixel electrode or the surface of the counter electrode and the large pretilt angle domain is so conditioned as to cause a larger pretilt angle of the liquid crystal molecules than the surrounding region does. This permits quick, reliable transition from a splay alignment state to the bend alignment state. Such transition is also facilitated by adding a chiral agent to a liquid crystal. A combination of the large pretilt angle domain and a chiral agent further facilitates occurrence of the transition. Another liquid crystal display device is designed such that the twist angle of the molecules of the liquid crystal ranges from 160° to 200° and that the fast response achieved by formation of an alignment state similar to the bend alignment state can be achieved without formation of the bend alignment state, by applying a driving voltage higher than the voltage, which causes the extremum of transmission in the driving voltage-transmission characteristic of the device, between the pixel and counter electrodes. In another liquid crystal display device, the pixels corresponding to the pixel electrode are divided into at least two domains which cause bend director fields having different orientations, thereby improving viewing angles. In still another liquid crystal display device, the twist angle of the molecules of the liquid crystal is in the range of from 160° to 200° or from 250° to 290° and the liquid crystal layer contains a dye or pigment. The device is driven with voltages in a certain high range. With this arrangement, the difficulty in causing the transition can be overcome. Another liquid crystal display device has pretilt angles varying according to the colors of pixels. This arrangement prevents hue shifts caused by changes in the transmission of the liquid crystal, the changes being due to the different wavelengths of transmitted light.

What is claimed is:  
     
         1 . A liquid crystal display device comprising (1) a pixel electrode, (2) a counter electrode and (3) a liquid crystal enclosed between the pixel and counter electrodes, 
 wherein the respective opposed surfaces of the pixel and counter electrodes are conditioned such that liquid crystal molecules contacting or in the vicinity of said surfaces have specified pretilt angles,    wherein images are displayed by changing light transmission through formation of a bend alignment state of the liquid crystal, and    wherein a large pretilt angle domain is formed on at least either one of said surfaces of the pixel and counter electrodes, the large pretilt angle domain causing a larger pretilt angle of liquid crystal molecules than a region surrounding the large pretilt angle domain does.    
     
     
         2 . A liquid crystal display device according to  claim 1 , wherein the pretilt angle of the liquid crystal molecules caused by the large pretilt angle domain is 10° or more larger than that caused by the surrounding region.  
     
     
         3 . A liquid crystal display device according to  claim 1 , wherein the pretilt angle of the liquid crystal molecules caused by the large pretilt angle domain is 15° or more.  
     
     
         4 . A liquid crystal display device according to  claim 3 , wherein the pretilt angle of the liquid crystal molecules caused by the large pretilt angle domain is 70° or more.  
     
     
         5 . A liquid crystal display device according to  claim 1 , wherein a plurality of said pixel electrodes are provided and at least one large pretilt angle domain is formed on each pixel electrode.  
     
     
         6 . A liquid crystal display device according to  claim 1 , wherein said large pretilt angle domain is formed by a surface alignment agent which causes a larger pretilt angle of the liquid crystal molecules than the surrounding region does.  
     
     
         7 . A liquid crystal display device according to  claim 1 , wherein said large pretilt angle domain is formed by a projection which causes a larger pretilt angle of the liquid crystal molecules than the surrounding region does.  
     
     
         8 . A liquid crystal display device according to  claim 1 , wherein said liquid crystal contains a chiral agent.  
     
     
         9 . A method for fabricating a liquid crystal display device which comprises (1) a pixel electrode, (2) a counter electrode and (3) a liquid crystal enclosed between the pixel and counter electrodes and wherein images are displayed by changing light transmission through formation of a bend alignment state of the liquid crystal, 
 said method comprising the steps of: 
 (a) forming a film made from a mixture of a first surface alignment agent and a second surface alignment agent on at least one of the surfaces of said pixel and counter electrodes, the first surface alignment agent causing a first pretilt angle of liquid crystal molecules in the vicinity of said pixel electrode or counter electrode, the second surface alignment agent causing a second pretilt angle larger than the first pretilt angle, and  
   (b) causing the phase separation of said first and second surface alignment agents contained in said film.    
     
     
         10 . A method for fabricating a liquid crystal display device which comprises (1) a pixel electrode, (2) a counter electrode and (3) a liquid crystal enclosed between the pixel and counter electrodes and wherein images are displayed by changing light transmission through formation of a bend alignment state of the liquid crystal, 
 said method comprising the steps of: 
 (a) forming an alignment film made from a first surface alignment agent on at least one of the surfaces of said pixel and counter electrodes, the first surface alignment agent causing a first pretilt angle of liquid crystal molecules in the vicinity of said pixel electrode or counter electrode, and  
 (b) partially forming an alignment film made from a second surface alignment agent on the alignment film made from the first surface alignment agent, the second surface alignment agent causing a second pretilt angle larger than the first pretilt angle.  
   
     
     
         11 . A liquid crystal display device comprising (1) a pixel electrode, (2) a counter electrode, (3) a liquid crystal enclosed between the pixel and counter electrodes, and (4) a phase compensating layer, 
 wherein images are displayed by changing light transmission through formation of a bend alignment state of the liquid crystal, and    wherein said liquid crystal contains a chiral agent.    
     
     
         12 . A liquid crystal display device according to  claim 11 , wherein said chiral agent produces a chiral pitch in said liquid crystal, said chiral pitch ranging from 5 μm to 100 μm.  
     
     
         13 . A liquid crystal display device according to  claim 11 , wherein said chiral agent produces a chiral pitch in said liquid crystal, said chiral pitch ranging from 7 μm to 40 μm.  
     
     
         14 . A liquid crystal display device comprising (1) a first substrate having a pixel electrode formed thereon, (2) a second substrate having a counter electrode formed thereon and positioned opposite the first substrate, (3) a liquid crystal enclosed between the first and second substrates, (4) a first polarizer and a second polarizer disposed so as to sandwich the first and second substrates, the polarizing axes of the first and second polarizers crossing at right angles, and (5) a driver circuit for applying driving voltage between the pixel electrode and the counter electrode, 
 wherein the liquid crystal molecules of said liquid crystal have a twist angle ranging from 160° to 200°, and    wherein said driver circuit applies driving voltage between the pixel and counter electrodes, the driving voltage being higher than the highest one of voltages that cause the maximal value of light transmission in the driving voltage-transmission characteristic of the liquid crystal display device.    
     
     
         15 . A liquid crystal display device comprising (1) a first substrate having a pixel electrode formed thereon, (2) a second substrate having a counter electrode formed thereon and positioned opposite the first substrate, (3) a liquid crystal enclosed between the first and second substrates, (4) a first polarizer and a second polarizer disposed so as to sandwich the first and second substrates, the polarizing axes of the first and second polarizers being parallel to each other, and (5) a driver circuit for applying driving voltage between the pixel electrode and the counter electrode, 
 wherein the liquid crystal molecules of said liquid crystal have a twist angle ranging from 160° to 200°, and    wherein said driver circuit applies driving voltage between the pixel and counter electrodes, the driving voltage being higher than the highest one of voltages that cause the minimal value of light transmission in the driving voltage-transmission characteristic of the liquid crystal display device.    
     
     
         16 . A liquid crystal display device according to  claim 14  or  15 , further comprising a phase compensating layer at least either between the first substrate and the first polarizer or between the second substrate and the second polarizer.  
     
     
         17 . A liquid crystal display device according to  claim 16 , wherein said phase compensating layer is a biaxial phase compensating film.  
     
     
         18 . A liquid crystal display device according to  claim 16 , wherein said phase compensating layer is a laminated film composed of a biaxial phase compensating film and a uniaxial phase compensating film.  
     
     
         19 . A liquid crystal display device according to  claim 14  or  15 , wherein the chiral pitch of said liquid crystal is not less than the thickness of the liquid crystal and not more than three times the thickness of the liquid crystal.  
     
     
         20 . A liquid crystal display device comprising (1) a pixel electrode, (2) a counter electrode and (3) a liquid crystal enclosed between the pixel and counter electrodes, 
 wherein images are displayed by changing light transmission through formation of a bend alignment state of the liquid crystal, and    wherein pixels corresponding to the pixel electrode are divided into at least two domains which cause bend director fields having different orientations in the liquid crystal.    
     
     
         21 . A liquid crystal display device according to  claim 20 , wherein the orientations of the bend director fields caused by the two domains cross at right angles.  
     
     
         22 . A liquid crystal display device according to  claim 20 , 
 wherein the pixel electrode and the counter electrode are respectively provided with an alignment film at their surfaces facing the liquid crystal, and    wherein each alignment film is divided into said domains which are conditioned so as to cause differently oriented director fields in the liquid crystal.    
     
     
         23 . A liquid crystal display device according to  claim 22 , wherein the pairs of opposed domains, one domain of each pair being formed on the alignment film of the pixel electrode and the other domain of each pair being formed on the alignment film of the counter electrode, are conditioned such that each pair of opposed domains form a pair of director fields, the director fields of each pair respectively including liquid crystal molecules aligned at pretilt angles in a plane perpendicular to a displaying plane such that the director fields of each pair are symmetric with respect to a plane that is parallel to the displaying plane and located in the middle of the distance between the pixel electrode and the counter electrode.  
     
     
         24 . A liquid crystal display device according to  claim 20 , further comprising a phase compensating layer formed on at least either the outer surface of the pixel electrode or the outer surface of the counter electrode, for optically compensating the director alignment of the liquid crystal molecules.  
     
     
         25 . A liquid crystal display device according to  claim 20 , wherein said liquid crystal contains a chiral agent.  
     
     
         26 . A method for fabricating a liquid crystal display device, 
 wherein images are displayed by changing light transmission through formation of a bend alignment state of a liquid crystal enclosed between a pixel electrode and a counter electrode, and    wherein alignment films are respectively formed on the surfaces of the pixel electrode and the counter electrode, the surfaces facing the liquid crystal, the alignment film on the pixel electrode and a portion of the alignment film on the counter electrode which portion corresponds to the pixel electrode being respectively divided into at least two domains having different conditioning directions by directing ultraviolet lights to two regions corresponding to the two domains to be formed, the ultraviolet lights being directed in different directions or having different polarizing directions.    
     
     
         27 . A liquid crystal display device comprising (1) a twisted liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, the liquid crystal layer having liquid crystal molecules twisted between said pair of substrates and (2) a polarizing plate disposed on either the light incoming side or light outgoing side of the liquid crystal cell, 
 wherein said polarizing plate is disposed such that its polarizing axis is substantially parallel to the longitudinal axis of the liquid crystal molecules on the interface of one of said pair of substrates, said substrate being on the light incoming side or light outgoing side,    wherein the twist angle of the liquid crystal molecules in said liquid crystal layer is in the range of from 160° to 200° and said liquid crystal layer contains a dye or pigment,    which has a voltage-brightness characteristic according to which when the voltage applied to said liquid crystal cell exceeds the Freedericksz threshold voltage of the liquid crystal, brightness first rises gently with a first gradient and then rises with a second gradient sharper than the first gradient, and    which performs image displaying with driving voltages at least higher than the voltage corresponding to the turning point where brightness changes from the first gradient to the second gradient.    
     
     
         28 . A liquid crystal display device comprising (1) a twisted liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, the liquid crystal layer having liquid crystal molecules twisted between said pair of substrates and (2) a polarizing plate disposed on either the light incoming side or light outgoing side of the liquid crystal cell, 
 wherein said polarizing plate is disposed such that its polarizing axis is substantially parallel to the longitudinal axis of the liquid crystal molecules on the interface of one of said pair of substrates, said substrate being on the light incoming side or light outgoing side,    wherein the twist angle of the liquid crystal molecules in said liquid crystal layer is in the range of from 250° to 290° and said liquid crystal layer contains a dye or pigment,    which has a voltage-brightness characteristic according to which when the voltage applied to said liquid crystal cell exceeds the Freedericksz threshold voltage of the liquid crystal, brightness first rises gently with a first gradient and then rises with a second gradient sharper than the first gradient, and    which performs image displaying with driving voltages at least higher than the voltage corresponding to the turning point where brightness changes from the first gradient to the second gradient.    
     
     
         29 . A liquid crystal display device comprising (1) a twisted liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, the liquid crystal layer having liquid crystal molecules twisted between said pair of substrates and (2) a polarizing plate disposed on either the light incoming side or light outgoing side of the liquid crystal cell, 
 wherein said polarizing plate is disposed such that its polarizing axis is substantially parallel to the longitudinal axis of the liquid crystal molecules on the interface of one of said pair of substrates, said substrate being on the light incoming side or light outgoing side,    wherein the twist angle of the liquid crystal molecules in said liquid crystal layer is in the range of from 160° to 200° and said liquid crystal layer contains a dye or pigment,    which performs image displaying with driving voltages which permit the average tilt angle of liquid crystal directors relative to the plane of the substrates to be 10° or more.    
     
     
         30 . A liquid crystal display device comprising (1) a twisted liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, the liquid crystal layer having liquid crystal molecules twisted between said pair of substrates and (2) a polarizing plate disposed on either the light incoming side or light outgoing side of the liquid crystal cell, 
 wherein said polarizing plate is disposed such that its polarizing axis is substantially parallel to the longitudinal axis of the liquid crystal molecules on the interface of one of said pair of substrates, said substrate being on the light incoming side or light outgoing side,    wherein the twist angle of the liquid crystal molecules in said liquid crystal layer is in the range of from 250° to 290° and said liquid crystal layer contains a dye or pigment,    which performs image displaying with driving voltages which permit the average tilt angle of liquid crystal directors relative to the plane of the substrates to be 20° or more.    
     
     
         31 . A liquid crystal display device according to any one of  claims 27  to  30 , wherein said dye or pigment is black in color and image displaying is performed with driving voltages equal to and less than the Freedericksz threshold voltage of the liquid crystal only when black images are displayed.  
     
     
         32 . A liquid crystal display device comprising (1) a liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates which are rubbed in the same direction and (2) a polarizing plate disposed on either the light incoming side or light outgoing side of the liquid crystal cell, 
 wherein said polarizing plate is disposed with its polarizing axis being substantially parallel to the rubbing direction of said substrates,    wherein said liquid crystal layer contains a dye or pigment, and    wherein said liquid crystal cell is a bend director alignment cell in which a bend alignment state is formed at the time of application of voltage.    
     
     
         33 . A liquid crystal display device according to  claim 32 , wherein the bend alignment state formed at the time of application of voltage includes twist at the center of the liquid crystal cell.  
     
     
         34 . A liquid crystal display device according to claims  33 , wherein said liquid crystal contains a chiral agent.  
     
     
         35 . A liquid crystal display device comprising (1) a plurality of pixel electrodes constituting a plurality of pixels, (2) a counter electrode, (3) a liquid crystal enclosed between the pixel electrodes and the counter electrode, and (4) a color filter having regions respectively corresponding to said pixels, each region transmitting any one of a plurality of colors, 
 wherein at least either the surfaces of the pixel electrodes or the surface of the counter electrode is conditioned such that liquid crystal molecules in the vicinity of the surfaces or surface are aligned so as to form specified pretilt angles,    wherein images are displayed by changing light transmission through formation of a bend alignment state of said liquid crystal, and    wherein said specified pretilt angles vary according to the colors of the pixels.    
     
     
         36 . A liquid crystal display device according to  claim 35 , wherein said specified pretilt angles are determined such that when the same voltage is applied between the pixel electrodes for different colors and the counter electrode, the same transmission can be obtained for the pixels of different colors.