1. Field of the Invention
The invention relates to display devices, and more particularly to optically compensated bend mode liquid crystal display (OCB-LCD) devices capable of achieving high-speed response time and wide viewing angles and fabrication methods thereof.
2. Description of the Related Art
Liquid crystal display (LCD) devices have several advantages over other display technologies, such as a smaller volume, a lighter weight, and lower power consumption. As such, LCD devices are being applied in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and others. Given the trends, technological development of LCD device are now focusing on lighter and thinner profiles with increased portability.
However, for conventional LCD devices, due to a narrow viewing angle applications have been limited. To improve the viewing angle of LCD devices, multi-domain vertical alignment (MVA) LCD devices comprising of bumps or protrusions on substrate for creating different orientations of liquid crystal molecules have been introduced. Nonetheless, different liquid crystal orientations can cause electric field changes in a single liquid crystal cell, changes in liquid crystal alignment and changes in liquid crystal relaxation. In addition, forming bumps or protrusions on substrate requires a complex lithographic process utilizing a half-tone mask.
Another conventional method for improving the viewing angle of LCD devices is provided by changing orientations of liquid quid crystal molecules to achieve self-compensated viewing angles. This method improves response speed and widens viewing angles of LCD devices.
U.S. Pat. No. 6,950,172, the entirety of which is hereby incorporated by reference, discloses an optically compensated bend mode liquid crystal display (OCB-LCD) device. The OCB-LCD device is divided into multiple aligned domain regions and driven by an appropriate method to achieve a splay-to-bend mode transition boundary within a pixel region. Note that multiple aligned domain regions are conventionally formed by UV light illuminating on a photo-catalyst contained alignment layer. Alignment layer formed by photo-illumination requires multiple photo-mask processes and process of placing a photo-catalyst into the alignment layer, causing fabrication complexity.
The conventional OCB-LCD device 100 includes an array of pixel regions. Each pixel region is enclosed by data lines 113 and gate lines 114 as indicated in
When the conventional OCB-LCD device 100 is driven by appropriate procedure, liquid crystal molecules 120 and 121 exhibit splay-to-bend transition, thus creating a disclination line 123 between the sub-pixel regions I and II. The disclination line 123 is generated from a nucleus (indicated as 124 of
The conventional OCB-LCD device 100 however, requires adding a photo-catalyst or photo activator in the alignment layer, thus requiring expensive and intricate UV-light exposure machinery and equipment. Moreover, multiple photo-mask processes are also required, thus further increasing production costs.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
Embodiments of the invention provide an optically compensated bend mode liquid crystal display (OCB-LCD) device capable of achieving high-speed response time and wide viewing angles. By forming a protrusion structure and/or slit electrode structure in each pixel of the display device, multi-domains with different liquid crystal orientations are formed.
An exemplary embodiment of the invention provides an optically compensated bend (OCB) mode liquid crystal display (LCD) device, comprising a first substrate opposite a second substrate with a layer of liquid crystal molecules interposed therebetween. A first alignment layer is disposed on the first substrate. A second alignment layer is selectively disposed on a second region of the first alignment layer, exposing a first region of the first alignment layer. A third alignment layer is disposed on the second substrate. Orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different. When a voltage is applied to the OCB mode LCD device, a dual mode transition boundary is created between the first region and the second region.
Another exemplary embodiment of the invention provides an OCB mode LCD device, comprising a first substrate opposite a second substrate with a layer of liquid crystal molecules interposed therebetween. A first alignment layer is disposed on the first substrate. A second alignment layer is selectively disposed on a second region of the first alignment layer, exposing a first region of the first alignment layer. A third alignment layer is disposed on the second substrate. A fourth alignment layer is selectively disposed on a second region of the third alignment layer, exposing a first region of the third alignment layer. Orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different, and orientations of liquid crystal molecules on the third alignment layer and on the fourth alignment layer are different. When a voltage is applied to the OCB mode LCD device, a dual mode transition boundary is created between the first region and the second region.
The invention also provides a method for fabricating an OCB mode LCD device. A first substrate with an electrode structure thereon is provided. A first alignment layer is applied on the first substrate. A second alignment layer is printed on the second region of the first alignment layer, exposing a first region of the first alignment layer. A third alignment layer is applied on a second substrate. The first substrate and the second substrate are opposed. A layer of liquid crystal molecules is injected between the first substrate and the second substrate. Orientations of liquid crystal molecules on the first alignment layer and on the second alignment layer are different. When a voltage is applied to the OCB mode LCD device, a dual mode transition boundary is created between the first region and the second region.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
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.
Some exemplary embodiments of the invention provide a multiple aligned domain OCB-LCD device. Applying alignment layers with different surface characteristics in each pixel regions can achieve wide viewing angles of the OCB-LCD device. Note that although some embodiments are described in conjunction with examples of an OCB mode LCD, the features of these embodiments may also be applied to other mode LCD devices with multiple aligned domains.
Referring to
Note that the first patterned alignment layer 220 of
The first and the second alignment layers can be selected from materials with different polarities, as different polarities can cause different LC orientations due to surface tensions between the alignment layers and the LC layer.
According to an exemplary embodiment of the invention, the first alignment layer 220 preferably provides a vertical liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 75°-90° against the first alignment layer 220, while the second alignment layer 250 provides a horizontal liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-15° against the second alignment layer 250. Alternatively, the first alignment layer 220 provides a horizontal liquid crystal molecule orientation, i.e., a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-15° against the first alignment layer 220, while the second alignment layer 250 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 250.
The multiple aligned domain OCB-LCD devices of some embodiments of the invention are achieved by inkjet printing or rolling polyimide (PI) in conjunction with inkjet printing. The different alignment interfaces cause a disclination line between liquid crystal molecules in each sub-pixel region. Moreover, when the OCB-LCD device is driven by appropriate procedure, the disclination line becomes nucleation sites of splay-to-bend transition, thereby increasing viewing angles and accelerating phase transition speed.
An electrode layer is disposed on the first substrate 310 to serve as a pixel electrode controlling angled movement of liquid crystal molecules. A first alignment layer 340, such as commercial model SE-7492, is applied on a first region I of the first substrate 310. A bake process is then performed on the first substrate. A second alignment layer 350 is selectively disposed on a second region II of the first substrate 310. For example, the second alignment layer 350, such as commercial model SE-1410 diluted by γ-butylactone, is applied on a peripheral region of the first alignment layer (e.g., SE-7492). A baking process and a rubbing process are sequentially performed such that orientations of liquid crystal molecules on the first region I and on the second region II are different. Therefore, the first alignment layer 340 and the second alignment 350 separately provide the liquid crystal layer with different alignments and pre-tilt angles (as indicated as angle B and angle C). Angle B can be the same as or different from angle C. According to an exemplary embodiment of the invention, the first alignment 340 and the second alignment layer 350 can be separately formed by printing or inkjet printing on the first region I and the second region II of the first substrate 310. The first alignment 340 and the second alignment layer 350 can comprises polyvinyl alcohol (PVA), polyimide (PI), polyamide (PA), polyurethane (PU), nylon, silicon, or lecithin. Alternatively, the second alignment layer comprises an organic solvent, such as ethanol, isopropanol, n-methyl pyrrolidone, m-cresol, γ-butylactone, n,n-dimethylacetamide, n,n-dimethylformamide, ethylene glycol monobutyl ether, or diethylene glycol monoethyl ether.
The first region I of the first substrate 310 is a pixel region, while the second region II is a peripheral region. Alternatively, the first region I of the first substrate 310 is a peripheral region, while the second region is a pixel region. The peripheral region comprises a black matrix region, a gate line region, a data line region, an active device region, a contact hole region, and a slit region. Furthermore, according to another embodiment of the invention, the first region is a portion of a pixel region, while the second region is another portion of the pixel region.
The second substrate 320 includes a black matrix (BM) and a color filter structure thereon. An electrode is disposed on the color filter structure to serve as a common electrode controlling angled movement of liquid crystal molecules. A third alignment 330, such as commercial model SE-7492, is applied on the electrode. A baking process and a rubbing process are sequentially performed such that pre-tilt angles (indicated as angle A) of liquid crystal molecules on the third alignment layer is about 4°-5°. The third alignment 330 can comprises polyvinyl alcohol (PVA), polyimide (PI), polyamide (PA), polyurethane (PU), nylon, silicon, or lecithin.
According to an exemplary embodiment, the first alignment layer 340 can provide horizontal orientation to the liquid crystal layer 360 such that a longitudinal axis of the liquid crystal molecule is pre-tilted about 0°-15° (as indicated as angle B) against the first alignment layer 340. The second alignment layer 350 provides a vertical liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted about 75°-90° (as indicated as angle B) against the second alignment layer. Furthermore, the third alignment layer 330 provides a horizontal liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted about 0°-15° (as indicated as angle A) against the second alignment layer.
Alternatively, the first alignment layer 340 provides a horizontal liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-10° against the first alignment layer 340. Conversely, the second alignment layer 350 provides a horizontal liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-9° against the second alignment layer 350. Furthermore, the first alignment layer 340 can provide a horizontal liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-7° against the first alignment layer. Conversely, the second alignment layer provides a horizontal liquid crystal molecule orientation such that a longitudinal axis of the liquid crystal molecule is pre-tilted 0°-4° against the second alignment layer.
Since the different alignment interfaces between regions I and II cause a disclination line between boundary region 370, when the OCB-LCD device is driven by appropriate procedure, liquid crystal molecules 360a and 360b adjacent to the disclination line become nucleation sites of splay-to-bend transition, thereby accelerating phase transition speed and increasing viewing angles due to multiple aligned domains.
The invention is advantageous in that different pre-tilt angles and/or multiple aligned domain regions of OCB-LCD devices can be achieved by multiply applying different alignment layers on different regions. Optically compensated bend (OCB) mode liquid crystal material is less affected by liquid crystal liquidity and splay-to-bend transition of liquid crystal molecules is shortened due to high per-tilt angles, resulting in faster response speed, accelerating phase transition speed and increasing viewing angles due to multiple aligned domains 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, brightness, contrast ratio, and aperture of the LCD device.
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.
Number | Date | Country | Kind |
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TW95146839 | Dec 2006 | TW | national |