Abstract:
Substrate structures, liquid crystal display devices and methods of fabricating liquid crystal display devices. A substrate structure comprises a transparent substrate having an electrode layer thereon. A first alignment layer is formed on the transparent substrate. A second alignment layer is selectively formed on the first alignment, wherein alignment orientations of liquid crystal molecules on the first and second alignment layers are different.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to liquid crystal display (LCD) devices, and in particular to substrate structures for LCD devices 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 due to liquid crystal displays feature lighter weight, thinner profile, and increased portability are applicable in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and the like.  
         [0005]     A silicon oxide (SiO x ) layer is formed as an alignment layer in conventional optical compensated birefringence (OCB) mode LCD devices to improve viewing angle. The orientation of the silicon oxide (SiO x ) layer is determined during deposition, thereby the pre-tilt angle of liquid crystal molecules is controlled to a range between 30-60 degrees. The silicon oxide (SiO x ) layer, however, must be deposited in a vacuum, resulting in intricate fabrication procedures and reduced throughput.  
         [0006]     Additionally, luminance of conventional transflective LCDs are different in transmission mode and reflection mode, leading to unsaturated images. The alignment layers in reflection and transmission regions are different to meet different pre-tilt requirements of the liquid crystal layer. For example, conventional addition of photo-catalyst in polyimide (PI) and selective exposure due to photo-chemical reaction can create different orientation alignment layers.  
         [0007]      FIG. 1  is a schematic view of a conventional transflective LCD device with different orientation in the reflection and transmission regions. In  FIG. 1 , a transflective LCD comprises a lower substrate  11  such as an active device matrix substrate, an opposing upper substrate  12  with color filters  15  thereon, and a liquid crystal layer  13  interposed between the upper and lower substrates. The lower substrate  11  includes an active device array such as a thin film transistor (TFT) array on a transparent substrate. A display area of the lower substrate  11  can be divided into a reflection region R and a transmission region T. A transparent electrode  19  is formed on the lower substrate  11  and electrically connected to the thin film transistor (TFT) via a contact  20 . A reflective electrode  18  is deposited on the transparent electrode  19  in the reflection region R. A vertically oriented alignment layer  21  and a horizontally oriented alignment layer  22  are respectively disposed in the reflection region R and transmission region T of the lower substrate  11 . In conjunction with a horizontal oriented alignment  22  on the upper substrate  12 , different optical characteristics in reflective region R and in transmission region R can thus be achieved in a transflective LCD device.  
         [0008]     U.S. Pat. No. 6,862,058, the entirety of which is hereby incorporated by reference, discloses a transflective liquid crystal display with different alignment orientations in the reflection region and in the transmission region. Different alignment layers are separately formed in the reflection region and in the transmission region to improve viewing angle. Forming different alignment layers, however, requires intricate lithographic processes, leading to high production cost and low yield.  
         [0009]     Japanese Patent No. 7-92 467, the entirety of which is hereby incorporated by reference, discloses a liquid crystal display device with wide viewing angle. In each pixel region, different alignment layers are formed by lithography and etching, leading to high production cost and low yield.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     A detailed description is given in the following embodiments with reference to the accompanying drawings.  
         [0011]     Accordingly, different pre-tilt angles and/or multiple alignment regions of liquid crystal molecules in a single LCD device, such as a multi-domain vertical alignment (MVA) mode LCD, an optically compensated birefringence (OCB) mode LCD, or a transflective mode LCD, are desired to improve viewing angle, brightness, contrast ratio, and aperture of the LCD device.  
         [0012]     According to an embodiment of the invention, a substrate structure for a liquid crystal display device is provided. The substrate structure comprises a substrate with an electrode layer thereon, a first alignment layer disposed on the substrate, and a second alignment layer selectively disposed on the first alignment layer, wherein orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different.  
         [0013]     According to another embodiment of the invention, a liquid crystal display device comprises a first substrate, a second substrate opposing the first substrate, and a liquid crystal layer interposed between the first and the second substrates. The first substrate includes an electrode layer thereon. A first alignment layer is disposed on the first substrate. A second alignment layer is selectively disposed on the first alignment layer, wherein orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different.  
         [0014]     According to another embodiment of the invention, a method for fabricating a liquid crystal display device is provided. A substrate with an electrode layer thereon is provided. A first alignment layer is applied on the substrate. A second alignment layer selectively formed on the first alignment layer by inkjet printing, wherein orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different. 
     
    
     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 schematic view of a conventional transflective LCD device with different orientation in the reflection and transmission regions;  
         [0017]      FIG. 2  is schematic view of applying an alignment layer on a substrate according to an embodiment of the invention;  
         [0018]      FIG. 3  is a plan view illustrating the patterned alignment layer on a substrate formed by the step as shown in  FIG. 2 ;  
         [0019]      FIG. 4  is a cross section of forming a second alignment layer on the first patterned alignment layer according to an embodiment of the invention;  
         [0020]      FIG. 5  is a cross section of a second patterned alignment layer on the first patterned alignment layer according to an embodiment of the invention; and  
         [0021]      FIG. 6  is a cross section of a liquid crystal display device including a substrate of  FIG. 5  according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     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.  
         [0023]      FIG. 2  is schematic view of applying an alignment layer on a substrate according to an embodiment of the invention. The alignment layer may comprise polyvinyl alcohol (PVA), polyimide (PI), polyamide (PA), polyurea (PU), nylon, or lecithin. The alignment layer is preferably applied by a roller on a large scale substrate.  
         [0024]     Referring to  FIG. 3 , a substrate  130  with an electrode layer or other elements such as color filters (not shown) is provided. The substrate  130  comprises a glass substrate, metal substrate, or a transparent plastic substrate. The substrate  130  further comprises an array of active control devices including thin film transistors (TFTs). The electrode comprises organic conductive material or inorganic conductive material. Alternatively, the substrate  130  can be an opposing substrate with a color filter layer thereon. Sequentially, a relief (or anastatic) printing plate with predetermined patterns is attached on a roller  110 . A first patterned alignment layer  120  is preferably applied by the roller  110  on a large scale substrate  130 .  
         [0025]     Note that the first patterned alignment layer  120  of  FIG. 3  is not limited to representing the entire display region of an LCD device. The first patterned alignment layer  120  may represent only a single pixel region or a plurality pixel regions.  
         [0026]      FIG. 4  is a cross section of forming a second alignment layer on the first patterned alignment layer according to an embodiment of the invention. Referring to  FIG. 4 , a second alignment layer  150 ′ is preferably applied on the first patterned alignment layer  120  by inkjet printing. For example, a fluid injector device  140 , such as a thermal bubble driven inkjet printhead or a piezoelectric diaphragm driven inkjet printhead, can inject droplets  150  of alignment material on the first alignment layer  120 . The location and dimensions of the second alignment layer  150 ′ can be achieved by controlling the position of the fluid injector device  140  and the volume of the droplet  150 . The second alignment layer may comprise polyvinyl alcohol (PVA), polyimide (PI), polyamide (PA), polyurea (PU), nylon, or lecithin. An aligning procedure such as rubbing is subsequently performed after an 180° C. baking procedure.  
         [0027]      FIG. 5  is a cross section of a second patterned alignment layer on the first patterned alignment layer according to an embodiment of the invention. In  FIG. 5 , the second alignment material  150 ′ is precisely printed at predetermined sites on the first alignment layer  120 , exposing part of the first alignment layer  120 . By selecting different materials for the first and the second alignment layers, different liquid crystal orientations can be achieved in a single LCD device, thereby widening the viewing angle.  
         [0028]     Accordingly, the relationship between the first and the second alignment layers depends on types of the LCD device, such as a multi-domain vertical alignment (MVA) mode LCD, an optically compensated birefringence (OCB) mode LCD, or a transflective mode LCD. For example, when applying to a transflective mode LCD, the second alignment layer  150 ′ is disposed on the reflection region, exposing the first alignment layer  120  at the transmission region. By selecting different materials for the first and the second alignment layers, different liquid crystal orientations can be achieved corresponding to the transmission and reflection regions separately, thereby improving display quality of the transflective LCD device.  
         [0029]     Alternatively, the first and the second alignment layers can be selected from materials with different polarities, as different polarities can cause different liquid crystal orientations due to surface tensions between the alignment layers and the liquid crystal layer.  
         [0030]     According to an embodiment of the invention, the first alignment layer  120  preferably provides a vertical liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 75-90 degrees against the first alignment layer  120 , while the second alignment layer  150 ′ provides a horizontal liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 0-15 degrees against the second alignment layer  150 ′. Alternatively, the first alignment layer  120  provides a horizontal liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 0-15 degrees against the alignment layer  70 , while the second alignment layer  150 ′ provides a vertical liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 75-90 degrees against the second alignment layer  150 ′.  
         [0031]      FIG. 6  is a cross section of a liquid crystal display device including a substrate of  FIG. 5  according to an embodiment of the invention. Referring to  FIG. 6 , a liquid crystal display device  100  comprises a first substrate  130 , a second substrate  180  opposing the first substrate  130 , and a liquid crystal layer  145  interposed between the first substrate  130  and the second substrate  180 . The first substrate  130  comprises an electrode layer (not shown) to serve as a pixel electrode controlling liquid crystal molecule orientations. A first alignment layer  120  is disposed on the first substrate  130 . A second alignment layer  150 ′ is selectively disposed on the first alignment layer  120 , exposing part of the first alignment layer  120 . The alignment orientations and pre-tilt angles of liquid crystal molecules on the first alignment layer  120  and on the second alignment layer  150 ′ are different.  
         [0032]     The first substrate  130  comprises an electrode layer (not shown) to serve as a common electrode controlling liquid crystal molecule orientations. A third alignment layer  170  is disposed on the second substrate  180 . A fourth alignment layer  160  is selectively disposed on the third alignment layer  170 , exposing part of the third alignment layer  170 . The alignment orientations and pre-tilt angles of liquid crystal molecules on the third alignment layer  170  and on the fourth alignment layer  160  are different.  
         [0033]     The invention is advantageous in that different pre-tilt angles and/or multiple alignment regions of liquid crystal molecules in a single LCD device, such as a multi-domain vertical alignment (MVA) mode LCD, an optically compensated birefringence (OCB) mode LCD, or a transflective mode LCD, can be achieved. Moreover, different alignment materials can be applied by different methods including relief (or anastatic) printing and inkjet printing at different regions, thereby improving viewing angle, bright, contrast ratio, and aperture of the LCD device.  
         [0034]     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.