Atomic-beam alignment of inorganic materials for liquid-crystal displays

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Abstract

The technique used to align liquid crystals—rubbing the surface of a substrate on which a liquid crystal is subsequently deposited1,2,3—has been perfected by the multibillion-dollar liquid-crystal display industry. However, it is widely recognized that a non-contact alignment technique would be highly desirable for future generations of large, high-resolution liquid-crystal displays. A number of alternative alignment techniques have been reported4,5,6,7, but none of these have so far been implemented in large-scale manufacturing. Here, we report a non-contact alignment process, which uses low-energy ion beams impinging at a glancing angle on amorphous inorganic films, such as diamond-like carbon. Using this approach, we have produced both laptop and desktop displays in pilot-line manufacturing, and found that displays of higher quality and reliability could be made at a lower cost than the rubbing technique. The mechanism of alignment is explained by adopting a random network model of atomic arrangement in the inorganic films. Order is induced by exposure to an ion beam because unfavourably oriented rings of atoms are selectively destroyed. The planes of the remaining rings are predominantly parallel to the direction of the ion beam.

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Figure 1: A photograph of a laptop computer showing a 13.3 diagonal extended graphics array (XGA) thin-film transistor liquid-crystal display using a diamond-like carbon (DLC) film as the alignment layer.
Figure 2: Transmission of light through polyimide and the DLC films on glass substrates and in cells filled with liquid crystals.
Figure 3: The pre-tilt angle of the liquid crystal as a function of the angle of incidence of the ion beam and time of exposure.
Figure 4: The transmission contrast ratio contours measured as a function of viewing angle for one- and two-domain nematic liquid crystal cells.

References

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Acknowledgements

We thank T. Hashimoto for his encouragement and T. Ueki, H. Yamaguchi and M. Mitsuhashi for their sustained suport. P.C. thanks N. Okazaki for describing this technology to colleagues in Japan. G. Thompson photographed Figure 1.

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Correspondence to P. Chaudhari.

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