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Science & Technology News
New alignment technologies promise vast improvements
Two groups have recently published research into two new and improved techniques for surface alignment in LCD displays. Traditionally, liquid crystal surface alignment has been created by 'rubbing' a polymer layer in the direction of alignment. This not only has the disadvantage of being a contact technique, but in the industrial process of making displays, rubbing requires the display to be removed from the manufacturing line. Published in Science (291, 2576) Baek-woon Lee and Noel Clark from the University of Colorado have developed a lithographic technique of etching away an electrode pattern in a silicon based monolayer. 'Liquid-crystal alignment is achievable without molecular anisotropy or roughness', they said. 'Lithographically dividing a surface into two molecularly smooth isotropic regions produces alignment that is governed by the boundary lines between them'. Lee and Clark have produced similar results using microcontact printing and are keen to take their research further. 'We believe that any complex pattern of nematic alignment can be easily fabricated at micrometer resolution', they said. 'But to make effective devices, comparable results must be obtained on indium tin oxide and other transparent conducting substrates'. Researchers from IBM's laboratories in New York (T.J. Watson Research Center, Yorktown Heights, NY), California (Almaden Research Center, San Jose, CA) and Japan (Yamato Development Laboratory, Yamato, Japan) have used a low energy Ion beam to create surface alignment. In developing their contact-free alignment technique Chaudhari and colleagues decided to swap the usual polymer alignment film for a diamond-like carbon film. 'We have replaced the polyimide film with a one-step evaporated or sputtered [diamond-like carbon] film, which is deposited at room temperature', the team reported in Nature (411, 56-59). 'This is not only cost-effective, but also more environmentally friendly'. By directing a low-energy ion beam at the film, the researchers were able to selectively rearrange atoms across the film before bringing the layer in contact with the liquid crystal to align the crystal molecules. They were also able to tilt the molecules by up to 10 to optimize the display's contrast. The team believes that their technique will eventually outstrip conventional rubbing in terms of cost and quality of the display. 'We have already produced a high-resolution 22-inch display in a manufacturing environment using this process', said Chaudhari. 'We have found that more reliable and better-quality displays could be made at a lower cost than using the rubbing technique'. The first public demonstration of the prototype display was conducted at the annual meeting of the Society of Information Display, which was held June 3-8, 2001 in San Jose, California. The paper recently published in Nature (May 3 2001) is the first of four papers on different aspects of the technology.
Date: July 2001
Link: http://www.ibm.com
Source: IBM website
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