Abstract:
A reflective liquid crystal display device integrating a self-emitting display element and fabrication methods thereof. The reflective liquid crystal display integrating a self-emitting display element comprises a reflective liquid crystal display (LCD) device and a transparent self-emitting display element directly disposed on the reflective LCD device. The reflective LCD includes a reflective cholesterol liquid crystal display, a reflective polymer dispersed liquid crystal display, a reflective twisted nematic liquid crystal display, a reflective smectic liquid crystal display, a vertical aligned liquid crystal (VA-LC) display, or a ferro-electric liquid crystal display.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to liquid crystal display (LCD) devices and fabrication methods thereof, and in particular to reflective liquid crystal display devices integrating self-emitting display elements and fabrication methods thereof.  
         [0003]     2. Description of the Related Art  
         [0004]     Liquid crystal display (LCD) devices have many advantages such as small volume, light weight and low power consumption, and are applicable in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and the like, due to their lighter weight, thinner profile, and increased portability. Conventional reflective liquid crystal displays, however, can not achieve desirable brightness and contrast ratio in a dark ambience.  
         [0005]     As self-emitting display technologies develop, display luminance has improved. For example, organic light emitting display (OLED) devices have more efficient power consumption. A self-emitting display device, however, can be washed out in a bright ambience causing low contrast images. Accordingly, a reflective liquid crystal display device integrating a self-emitting device is required in both dark and bright ambiences.  
         [0006]     U.S. Publication No. 2004/0164292, the entirety of which is hereby incorporated by reference, discloses a reflective liquid crystal display device integrating a self-emitting device, using an organic light emitting display as a backlight unit of the reflective liquid crystal display device to improve brightness and contrast ratio in a dark ambience.  FIG. 1  is a cross section of a conventional reflective liquid crystal display device integrating a self-emitting display element. Referring to  FIG. 1 , a reflective electrode  22 , an organic light emitting layer  24 , and a transparent electrode  26  are sequentially formed on a substrate  10 . A self-emitting element  20  including the reflective electrode  22 , the organic light emitting layer  24 , and the transparent electrode  26  serves as a backlight unit of the reflective liquid crystal display device. A passivation layer  28  is formed on the transparent electrode  26 .  
         [0007]     A liquid crystal display  30  including a first polarizer  31  is disposed on the second substrate  32 . A pixel electrode  33  is disposed on the second substrate  32 . A third substrate  36  opposing the second substrate  32  has a common electrode  35  thereon. A liquid crystal layer is interposed between the second substrate  32  and the third substrate  36 . A second polarizer  37  is disposed on the third substrate  37 . In transmission mode, light emitted from the self-emitting display element  20  passes through the reflective liquid crystal display  30  to display images. In reflection mode, incident light  62  passing through the reflective liquid crystal display  30  is reflected by a reflective electrode  22 . Reflective light  63  then passes through the reflective liquid crystal display  30  to display images.  
         [0008]     U.S. Publication No. 2002/0196387 and U.S. Publication No. 2003/0201960, the entirety of which are hereby incorporated by reference, disclose a reflective liquid crystal display disposed on a self-light emitting display element. In a dark ambience, however, the self-emitting display element emits light passing through the liquid crystal layer, color filters and polarizers, causing deviation of emitted light. Conversely, in a bright ambience, the self-light emitting display element serves as a reflector and reflects incident light passing through the liquid crystal device. The incident light, however, can be absorbed by the liquid crystal layer and the absorption of the liquid crystal layer in both bright and dark states can be different, causing variation of contrast ratio. Display quality in conventional reflective liquid crystal display devices suffers due to absorption of incident light.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     A detailed description is given in the following embodiments with reference to the accompanying drawings.  
         [0010]     Accordingly, a stacked reflective liquid crystal display device integrating a self-emitting display element is provided. The self-emitting display element is disposed on the reflective liquid crystal display device to prevent washout effect in a bright ambience and improve contrast ratio of the display device in a dark ambience.  
         [0011]     An exemplary embodiment of a reflective liquid crystal display device integrating a self-emitting display element comprises a reflective liquid crystal display element, and a transparent self-emitting display element directly disposed on the reflective liquid crystal display element. The reflective liquid crystal display element comprises a first substrate with an absorption layer thereon, a first transparent electrode disposed on the absorption layer, a cholesterol mode liquid crystal layer disposed on the first transparent electrode, a second transparent electrode disposed on the cholesterol mode liquid crystal layer, and a second substrate disposed on the second transparent electrode.  
         [0012]     Another exemplary embodiment of a reflective liquid crystal display device integrating a self-emitting display element comprises: a substrate with a reflective layer thereon; a first transparent electrode disposed on the reflective layer; a reflective liquid crystal layer disposed on the first transparent electrode; and a second transparent electrode disposed on the cholesterol mode liquid crystal layer. A passivation layer is disposed on the second transparent electrode. A transparent self-emitting display element is disposed on the passivation layer comprising a third electrode disposed on the passivation layer, a light emitting layer disposed on the third electrode, a fourth electrode disposed on the light emitting layer, and a second substrate disposed on the fourth electrode.  
         [0013]     According to another embodiment of the invention, a method for fabricating a reflective liquid crystal display device integrating a self-emitting display element is provided. A substrate with an optical-function layer thereon is provided. A first transparent electrode is formed on the optical-function layer. A reflective liquid crystal layer is applied on the first transparent electrode. A second transparent electrode is formed on the reflective liquid crystal layer. A passivation layer is formed on the second transparent electrode. A third electrode is disposed on the passivation layer. A light emitting layer is formed on the third electrode. A fourth electrode is formed on the light emitting layer.  
         [0014]     According to another embodiment of the invention, a method for fabricating a reflective liquid crystal display device integrating a self-emitting display element is provided. A first substrate with a transparent self-emitting display element thereon is provided. A passivation layer is formed on the transparent self-emitting display element. A first electrode is formed on the passivation layer. A second substrate with a second electrode thereon is provided. The first substrate is assembled opposing the second substrate with a gap therebetween. A liquid crystal layer is injected between the first and the second substrates. An optical-function layer is formed on the second substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0016]      FIG. 1  is a cross section of a conventional reflective liquid crystal display device integrating self-emitting display element;  
         [0017]      FIG. 2A  is a stereographical view of a reflective liquid crystal display device integrating a self-emitting display element according to an embodiment of the invention;  
         [0018]      FIG. 2B  is a schematic view of the reflective liquid crystal display device of  FIG. 2A  in the “on” state;  
         [0019]      FIG. 3  is a flowchart of a fabrication method of a reflective liquid crystal display device integrating a self-emitting display element according to an embodiment of the invention;  
         [0020]      FIG. 4  is a stereographical view of the reflective liquid crystal display device formed by the fabrication method of  FIG. 3 ;  
         [0021]      FIG. 5  is a flowchart of a fabrication method of a reflective liquid crystal display device integrating a self-emitting display element according to another embodiment of the invention;  
         [0022]      FIG. 6  is a stereographical view of the reflective liquid crystal display device formed by the fabrication method of  FIG. 5 ; and  
         [0023]      FIG. 7  is a stereographical view of an organic light emitting display element according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.  
         [0025]      FIG. 2A  is a stereographical view of a reflective liquid crystal display device integrating a self-emitting display element according to an embodiment of the invention. Referring to  FIG. 2A , a reflective liquid crystal display element  120  is disposed on a first substrate  110 . The reflective liquid crystal display element  120  comprises a reflective cholesterol mode liquid crystal display, a polymer dispersed liquid crystal (PDLC) display, a reflective twisted nematic (TN) mode liquid crystal display, a reflective sematic liquid crystal display, a vertical aligned liquid crystal (VA-LC) display, or a reflective ferroelectric liquid crystal display.  
         [0026]     An optical-function layer  122  comprising a reflective layer or an absorption is disposed on the first substrate  110 . A first transparent electrode  124  is disposed on the optical-function layer  122 . A reflective liquid crystal layer  126  is disposed on the first transparent electrode  124 . A second transparent electrode  128  is disposed on the cholesterol mode liquid crystal layer  126 . According to an embodiment of the invention, the reflective liquid crystal display element  120  can further comprise a second substrate (not shown) on the second transparent electrode  128 . Alternatively, the second substrate can be a passivation layer, a thin film stacking alyer, a glass substrate, or a plastic substrate disposed on the second transparent electrode  128 . Moreover, the reflective liquid crystal display element  120  can further comprise a phase retardation film, a color filter and/or a polarizer on the second substrate.  
         [0027]     A transparent self-emitting display element  130  is directly disposed on the reflective liquid crystal display element  120 . The transparent self-emitting display element  130  comprises a third electrode  132  disposed on the reflective liquid crystal display element  120 . A light-emitting layer  134  is disposed on the third electrode  132 . A fourth electrode  136  is disposed on the light-emitting layer  134 . According to an embodiment of the invention, the transparent self-emitting display element  130  can further comprise a carrier injection layer interposed between the third electrode  132  and the light-emitting layer  134 . Moreover, another carrier injection layer can be interposed between the light-emitting layer  134  and the fourth electrode  136 .  
         [0028]     The reflective liquid crystal display device integrating a self-emitting display element may further comprise an array of micro-lens structures or a micro-optical grating disposed on the transparent self-emitting display element  130 .  
         [0029]     In  FIG. 2A , when the reflective liquid crystal display element  120  is switched off, the liquid crystal molecules  125  of the liquid crystal layer  126  is randomly dispersed. Incident ambient light  161  passes through the transparent self-emitting display element  130  and is scattered by randomly dispersed liquid crystal molecules  125 , and further absorbed by the absorption layer  122 , thus displaying a “dark” state.  
         [0030]      FIG. 2B  is a schematic view of the reflective liquid crystal display device of  FIG. 2A  in the “on” state. In  FIG. 2B , when the reflective liquid crystal display element  120  is switched on, the liquid crystal molecules  125  of the liquid crystal layer  126  is regularly aligned with the applied electric field. Incident ambient light  162  passes through the liquid crystal layer  126  and is reflected by regularly aligned liquid crystal molecules  125  (reflective light  163  in  FIG. 2A ), thus displaying a “bright” state.  
         [0031]     Accordingly, the transparent self-emitting display element  130  directly disposed on the reflective liquid crystal display element  120  is advantageous in that when ambient light is dark, the transparent self-emitting display element  130  serves as a primary display element. The self-emitting display element  130  emits light without passing through the reflective liquid crystal display element  120 . Additional polarizers and color filters are unnecessary, and the display quality is not affected due to additional polarizers and color filters. On the other hand, when ambient light is bright, the reflective liquid crystal display element  120  serves as a primary display element. Although the ambient light must pass through the transparent self-emitting display element  130  and the reflective liquid crystal display element  120  causing absorption of the ambient light. The absorption of the ambient light, however, does not affect image contrast ratio and power consumption of the display device.  
         [0032]     Note that the reflective liquid crystal display device integrating a self-emitting display element according to an embodiment of the invention does not limit to reflective liquid crystal display elements. Other liquid crystal display elements or light modulating devices are also applicable thereto. Moreover, the transparent self-emitting display element comprises an organic light emitting display element or an inorganic light emitting display element.  
         [0033]      FIG. 3  is a flowchart of a fabrication method of a reflective liquid crystal display device integrating a self-emitting display element according to an embodiment of the invention.  FIG. 4  is a stereographical view of the reflective liquid crystal display device formed by the fabrication method of  FIG. 3 . In an aspect of the invention, an organic light emitting display element is formed before a reflective liquid crystal display element is formed.  
         [0034]     Referring to  FIGS. 3 and 4 , a first substrate  450  is provided in step S 310 . Next, in step S 312 , an organic light-emitting display element  440  is formed on the first substrate  450  comprising sequentially forming a transparent cathode on the first substrate  450 , forming an organic light emitting layer on the transparent cathode, and forming a transparent anode on the organic light emitting layer. In step S 314 , a passivation layer  430  is formed on the organic light-emitting display element  440 . Subsequently, in step S 316 , a transparent electrode  423  such as indium tin oxide (ITO) is formed on the passivation layer  430 . In step S 318 , an alignment layer  428  such as polyimide (PI) is applied on the transparent electrode  423  by roll coating.  
         [0035]     A second substrate  410  is provided in step S 322 . Subsequently, in step S 324 , a transparent electrode  422  such as indium tin oxide (ITO) is formed on the second substrate  410 . In step S 326 , an alignment layer  424  such as polyimide (PI) is applied on the transparent electrode  422  by roll coating.  
         [0036]     In step S 330 , the second substrate  410  is assembled opposing the first substrate  450  with spacers interposed therebetween to maintain a specific gap. Subsequently, in step S 340 , a liquid crystal layer  426  is injected between the first and second substrates and sealed. Next, an optical-function layer (not shown) is formed on the second substrate  410  in step S 350 , thus completing the reflective liquid crystal display device integrating a self-emitting display element.  
         [0037]      FIG. 5  is a flowchart of a fabrication method of a reflective liquid crystal display device integrating a self-emitting display element according to another embodiment of the invention.  FIG. 6  is a stereographical view of the reflective liquid crystal display device formed by the fabrication method of  FIG. 5 . In another aspect of the invention, a reflective liquid crystal display element is formed before an organic light emitting display element is formed.  
         [0038]     Referring to  FIGS. 5 and 6 , a substrate  410  is provided in step S 510 . Next, in step S 520 , an optical-function layer (not shown) is formed on the substrate  410 . Subsequently, in step S 530 , a transparent electrode  424  such as indium tin oxide (ITO) is formed on the substrate  410 . In step S 540 , an alignment layer (not shown) such as polyimide (PI) is applied on the transparent electrode  424  by roll coating.  
         [0039]     In step S 550 , patterned photoresist spacers  427  are formed on the alignment layer. The patterned photoresist spacers  427  can be wall structures dividing a plurality of pixel regions. In step S 560 , a liquid crystal layer  426  is formed on the alignment layer by inkjet printing. Subsequently, in step S 570 , a transparent electrode  423  such as indium tin oxide (ITO) is formed on the liquid crystal layer  426 . In step S 580 , a passivation layer  430  is formed on the transparent electrode  423 . In step S 590 , an organic light emitting display element  440  is formed on the passivation layer  430 , comprising sequentially forming a transparent cathode on the passivation layer, forming an organic light emitting layer on the transparent cathode, and forming a transparent anode on the organic light emitting layer.  
         [0040]      FIG. 7  is a stereographical view of an organic light emitting display element according to an embodiment of the invention. Referring to  FIG. 7 , an organic light emitting display element  440  comprises an anode  431  such as a transparent indium tin oxide (ITO) layer. A hole injection layer (HIL)  432  such as CuPc is formed on the anode  431 . A hole transportation layer (HTL)  433  such as NPB is formed on the hole injection layer (HIL)  432 . An organic light emitting layer  434  such as Alq 3  is formed on the hole transportation layer (HTL)  433 . An electron injection layer (EIL)  435  such as LiF is formed on the organic light emitting layer  434 . A cathode  436  such as Al and transparent electrode composite structure is formed on the electron injection layer (EIL)  435 .  
         [0041]     The invention is advantageous in that a stacked reflective liquid crystal display device integrating a self-emitting display element is provided. When the ambience is bright, a reflective image is displayed, and when the ambience is dark, an image is displayed by an organic light emitting display element. The backlight unit (BLU), color filters and polarizers can be omitted, thereby reducing production cost.  
         [0042]     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.