Patent Publication Number: US-2015077687-A1

Title: Liquid crystal display device

Description:
BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     The invention relates to a liquid crystal display device. 
     b. Description of the Related Art 
     In a conventional cholesteric liquid crystal display device, a red, a green and a blue cholesteric liquid crystal are separately driven to display a color image. As shown in  FIG. 1 , typically, the red cholesteric liquid crystal is driven at a voltage of about 30-40V, the green cholesteric liquid crystal is driven at a voltage of about 36-46V, and the blue cholesteric liquid crystal is driven at a voltage of about 38-50V. Therefore, the cholesteric liquid crystals of different colors are applied with respective voltage intervals. In that case, for example, a driving voltage interval for the red cholesteric liquid crystal is not suitable for the blue cholesteric liquid crystal. Therefore, three distinct driving voltages should be provided for the cholesteric liquid crystals of different colors to write grayscale pixel data and thus complicate the entire driving architecture. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a liquid crystal display device having simplified driving architecture. 
     According to an embodiment of the invention, a liquid crystal display device includes a first substrate, a second substrate opposite the first substrate, a fence structure, a plurality of cholesteric liquid crystals having mutually different color, and a medium layer. The fence structure is disposed between the first substrate and the second substrate to divide a space between the first substrate and the second substrate into different sub-pixel channels. The cholesteric liquid crystals are disposed into the sub-pixel channels to form different liquid crystal cells having mutually different colors. The medium layer is disposed in at least one of the sub-pixel channels to allow the liquid crystal cells to have mutually different cell gaps. 
     According to another embodiment of the invention, a liquid crystal display device includes a first substrate, a second substrate opposite the first substrate, a fence structure, a plurality of cholesteric liquid crystals having mutually different color, and a plurality of medium layers. The fence structure is disposed between the first substrate and the second substrate to divide a space between the first substrate and the second substrate into different sub-pixel channels. The cholesteric liquid crystals are disposed into the sub-pixel channels to form different liquid crystal cells having mutually different colors. The medium layers are respectively disposed in the sub-pixel channels and have mutually different dielectric constants. 
     According to another embodiment of the invention, a liquid crystal display device includes a first substrate, a second substrate opposite the first substrate, a fence structure, a plurality of cholesteric liquid crystals having mutually different color, and a plurality of medium layers. The fence structure is disposed between the first substrate and the second substrate to divide a space between the first substrate and the second substrate into at least a red sub-pixel channel, a green sub-pixel channel, and a blue sub-pixel channel. The cholesteric liquid crystals are respectively disposed inside the red sub-pixel channel, the green sub-pixel channel, and the blue sub-pixel channel to form a red liquid crystal cell, a green liquid crystal cell and a blue liquid crystal cell. The medium layers have mutually different dielectric constants and are disposed in the red sub-pixel channel and the green sub-pixel channel but not in the blue sub-pixel channel. 
     According to the above embodiments, the electric fields of different color cholesteric liquid crystals respectively in different sub-pixel channels may vary according to the different thicknesses, different material characteristics, or the existence of a medium layer in the different sub-pixel channels. Therefore, the cholesteric liquid crystals of different colors may be all driven by an identical voltage to thus simplify the entire driving architecture. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram illustrating different driving voltage curves for cholesteric liquid crystals of different colors. 
         FIG. 2  shows a schematic diagram of a liquid crystal display device according to an embodiment of the invention. 
         FIG. 3  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. 
         FIG. 4  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. 
         FIG. 5  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. 
         FIG. 6  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG. 2  shows a schematic diagram of a liquid crystal display device according to an embodiment of the invention. Referring to  FIG. 2 , the liquid crystal display device  10  includes a first substrate  12 , a second substrate  14  and a patterned fence structure  16 . The fence structure  16  is disposed between the first substrate  12  and the second substrate  14  and divides a space between the first substrate  12  and the second substrate  14  into different sub-pixel channels  18 , and multiple cholesteric liquid crystals  22  having mutually different colors are disposed into their respective sub-pixel channels  18  to form liquid crystal cells PR, PG and PB having mutually different colors. For example, in this embodiment, the red cholesteric liquid crystal  22 R is disposed into the red sub-pixel channel  18 R, the green cholesteric liquid crystal  22 G is disposed into the green sub-pixel channel  18 G, and the blue cholesteric liquid crystal  22 B is disposed into the blue sub-pixel channel  18 B. The fence structure  16  may include multiple partition walls  16   a  to divide the space between the first substrate  12  and the second substrate  14  into different sub-pixel channels  18 . Further, a medium layer  24  is disposed in the sub-pixel channels  18 R,  18 G and  18 B, and the medium layer  24  in the sub-pixel channels  18 R,  18 G and  18 B have mutually different thicknesses. In this embodiment, a transparent electrode layer  28   a  is disposed between the first substrate  12  and the fence structure  16 , and another transparent electrode layer  28   b  is disposed between the second substrate  14  and the fence structure  16 . An adhesive layer  32  may be disposed between the transparent electrode layer  28   a  and the fence structure  16  to avoid an overflow of any of the sub-pixel channels  18 . Note the adhesive layer  32  may be omitted from the liquid crystal display device  10 , and, in an alternate embodiment, a partition divided by the fence structure  16  may be encapsulated to form a sub-pixel channel  18 . The medium layer  24  may be disposed on the transparent electrode layer  28   b  and may include, for example, a black matrix  26   a  in the red sub-pixel channel  18 R, a black matrix  26   b  in the green sub-pixel channel  18 G, and a black matrix  26   c  in the blue sub-pixel channel  18 B. In this embodiment, a thickness of the black matrix  26   a  in the red sub-pixel channel  18 R is greater than a thickness of the black matrix  26   b  in the green sub-pixel channel  18 G, and a thickness of the black matrix  26   b  in the green sub-pixel channel  18 G is greater than a thickness of the black matrix  26   c  in the blue sub-pixel channel  18 B. 
     According to the above embodiments, since the black matrixes  26   a,    26   b  and  26   c  are respectively disposed in the sub-pixel channels  18 R,  18 G and  18 B at mutually different thicknesses, the liquid crystal cells PR, PG and PB may have mutually different cell gaps d. Typically, a voltage sufficient to drive a cholesteric liquid crystal may vary according to a value of the cell gap d. Therefore, according to the above embodiments, the black matrix  26   a,    26   b  and  26   c  are set to have proper and mutually different thicknesses to equalize the driving voltages needed for cholesteric liquid crystals of different colors. Under the circumstance, the cholesteric liquid crystals of different colors may be all driven by an identical voltage difference to write grayscale pixel data and thus simplify the entire driving architecture. 
       FIG. 3  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. Note the medium layer  24  is not limited to a specific material. In an alternate embodiment shown in  FIG. 3 , the medium layer  24  may be an organic insulation layer  34 , and a black matrix layer  26  is disposed on one side of the second substrate  14  facing away from the sub-pixel channels  18 . Further, the medium layer  24  is not limited to be disposed in each of the sub-pixel channels  18 . For example, in this embodiment, the organic insulation layer  34  of the liquid crystal display device  30  is disposed only in the red sub-pixel channel  18 R and the green sub-pixel channel  18 G but not disposed in the blue sub-pixel channel  18 B. Besides, a thickness of the organic insulation layer  34  in the red sub-pixel channel  18 R is greater than a thickness of the organic insulation layer  34  in the green sub-pixel channel  18 G. In that case, electric fields of cholesteric liquid crystals may vary according to the thickness or existence of the organic insulation layer  34  in a sub-pixel channel  18 . Therefore, the cholesteric liquid crystals of different colors (such as red, green and blue) may be all driven by an identical voltage difference. Alternatively, the medium layer  24  may be an inorganic insulation layer. In an alternate embodiment, the organic insulation layer  34  shown in  FIG. 3  may be replaced with the black matrix layer  26  to achieve similar effects. 
       FIG. 4  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. Referring to  FIG. 4 , in a liquid crystal display device  40 , the transparent electrode layer  28   a  is disposed between the first substrate  12  and the fence structure  16 , the transparent electrode layer  28   b  is disposed in the sub-pixel channels  18 , and the medium layer  24  is disposed on the second substrate  14 . In this embodiment, the medium layer  24  includes the black matrix  26   a  in the red sub-pixel channel  18 R, the black matrix  26   b  in the green sub-pixel channel  18 G, and the black matrix  26   c  in the blue sub-pixel channel  18 B. A thickness of the black matrix  26   a  is smaller than a thickness of the black matrix  26   b , and a thickness of the black matrix  26   b  is smaller than a thickness of the black matrix  26   c.  Therefore, electric fields of cholesteric liquid crystals may vary according to the different thicknesses of the black matrix  26 , and thus the cholesteric liquid crystals of different colors (such as red, green and blue) may be all driven by an identical voltage difference. 
       FIG. 5  shows a schematic diagram of a liquid crystal display device according to another embodiment of the invention. Referring to  FIG. 5 , a liquid crystal display device  50  has a medium layer  24   a  in the red sub-pixel channel  18 R, a medium layer  24   b  in the green sub-pixel channel  18 G, and a medium layer  24   c  in the blue sub-pixel channel  18 B. In this embodiment, the medium layers  24   a,    24   b  and  24   c  have mutually different dielectric constants. Therefore, electric fields of cholesteric liquid crystals may vary according to the different dielectric constants of the medium layers  24   a,    24   b  and  24  to drive cholesteric liquid crystals of different colors at an identical voltage difference, even the medium layers  24   a,    24   b  and  24  have the same thickness. Note, in this embodiment, the medium layers  24   a,    24   b  and  24   c  are not limited to a specific material. For example, each of the medium layers  24   a,    24   b  and  24   c  may be an organic insulation layer, an inorganic insulation layer, or a black matrix. Further, in an alternate embodiment shown in  FIG. 6 , a liquid crystal display device  60  has a medium layer  24   a  in the red sub-pixel channel  18 R and a medium layer  24   b  in the green sub-pixel channel  18 G, but the blue sub-pixel channel  18 B is not provided with a medium layer  24   c.  The medium layer  24   a  and the medium layer  24   b  may have an identical thickness but different dielectric constants. Therefore, electric fields of cholesteric liquid crystals may vary according to the different dielectric constants of the medium layers  24   a  and  24   b  or the existence of the medium layer  24   c  in a sub-pixel channel  18 , and thus the cholesteric liquid crystals of different colors (such as red, green and blue) may be all driven by an identical voltage difference. In one embodiment, each of the medium layer  24   a  and the medium layer  24   b  may be a black matrix or an insulation layer. As shown in  FIG. 6 , since the blue sub-pixel channel  18 B is not provided with a black matrix or an insulation layer, a black matrix layer  26  may be disposed on one side of the second substrate  14  facing away from the sub-pixel channels  18 . 
     According to the above embodiments, electric fields of cholesteric liquid crystals of different colors respectively in different sub-pixel channels may vary according to the different thicknesses, different material characteristics, or the existence of a medium layer in the different sub-pixel channels. Therefore, the cholesteric liquid crystals of different colors may be all driven by an identical voltage difference to thus simplify the entire driving architecture. 
     In one embodiment, each of the red cholesteric liquid crystal  22 R, the green cholesteric liquid crystal  22 G, and the blue cholesteric liquid crystal  22 B may include a corresponding colored pigment, a nematic liquid crystal with a chiral dopant, or a polymer dispersed liquid crystal. Further, the fence structure  16  may be formed form an organic or an inorganic material. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims. Each of the terms “first” and “second” is only a nomenclature used to modify its corresponding element. These terms are not used to set up the upper limit or lower limit of the number of elements.