Sharp Corp of Japan
has developed a new liquid crystal display mode dubbed UV2A, for
Ultraviolet-induced multi-domain Vertical Alignment. Liquid crystal
display (LCD) panels produced at the Sakai Plant, which began operation
in Oct 2009, and the Kameyama No. 2 Plant, will be switched to the new
technology. The company is now implementing a complete changeover from
Advanced Super View (ASV) mode panels for its televisions.
There are a number of liquid crystal display modes, depending on differences in liquid crystal material, drive method, etc. In addition to ASV, there are also modes such as super-twisted nematic (STN) and in-plane switching (IPS).
The most important difference between UV2A and conventional display modes is that UV radiation is used to control liquid crystal molecule alignment. Called photo-alignment technology, the concept has been known for 30 years and recognized as the ideal alignment method, according to a source at Sharp. At the technology announcement, the Sharp spokesman repeated several times that it had "finally realized the 30-year old dream of liquid crystal engineers."
There are four major merits in UV2A panels: lower power consumption, higher contrast ratio, faster response, and lower manufacturing cost (see Fig). Sharp plans to talk up UV2A as a core technology in its "Sakai model" LCD TVs.
Newly Developed
PolymerThe major technological breakthrough in commercializing photo-alignment technology was the newly developed polymer thinfilm (alignment film). When exposed to UV light, polymer chains align with the light beam. The polymer chains are used to control liquid crystal molecule alignment. A new exposure system was also developed to illuminate the polymer from the diagonal direction.
The liquid crystal molecule alignment process is extremely simple. The alignment film is coated on a glass substrate, and then just illuminated (exposed). Sharp claims that this process provides "extremely precise control," with an error of +/-20pm.
Photo-alignment technology has been called the "ideal alignment technology" because it resolves a number of problems found in conventional technologies. For example, the rib-slit alignment method currently used by Sharp in its ASV LCD panels creates minute structures called ribs and slits inside each pixel. Liquid crystal molecule inclination and the electric field distortion effort are used to control molecule alignment. These structures, however, reduce the aperture ratio of the pixel, often scattering light near themselves and causing light leaks. These problems all contribute to deterioration in optical utilization performance (power consumption) and contrast ratio.
Response speed was another point that needed to be improved upon. When voltage is applied, response begins from the liquid crystal molecules nearest the structures, gradually covering the entire area through a domino effect. Sharp says that with photo-alignment, which does not require these structures, this effect is eliminated.
Photo-alignment technology may have been commercialized after 30 years, but its impact on the market is as yet unknown. The reason is that it is difficult to implement without UV2A liquid crystal panels, and so far no application product has been released that really requires the technology. In addition, the market is already saturated with LCD application products and technical innovation is proceeding rapidly to improve the various problems found in other alignment technologies.
Until now, the development of a new liquid crystal display mode had also driven the development of new application products. The appearance of display modes like IPS and VA, delivering a wider viewing angle, provided a major impetus to the realization of LCD TVs. According to Shigeaki Mizushima, executive managing officer, group general manager, Corporate Research & Development Group of Sharp, "Photo-alignment technology offers excellent design freedom, and makes possible entirely new applications nobody has ever thought of before. In another ten years I think the impact of this technology will be obvious." It seems that the real worth of the technology will only become apparent after new application products emerge.
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