Abstract
We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium–tin oxide (ITO) layers with high resolution (ca< 20 nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner not only provides high anchoring energy comparable to that of rubbed polyimides, but also maintains its low resistivity as an electrode. As a result, the patterned ITO can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices. The LC cells fabricated using patterned ITO substrates show highly stable alignment of LCs over large area and good electro-optical responses. Moreover, systematic approach made by the precise control of pattern dimensions allows us to estimate a critical anchoring energy required for an effective LC alignment based on Berreman's theory.
Highlights
Conventional liquid crystal (LC) electro-optical devices incorporate separate layers of a transparent electrode and an organic polymer film for driving devices and controlling LC alignment, respectively
We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium–tin oxide (ITO) layers with high resolution and high aspect ratio, fabricated based on the secondary sputtering phenomenon
A slanting view of the scanning electron microscope (SEM) images clearly reveals that narrow lines of Indium–tin oxide (ITO) are well developed and regularly aligned on the flat ITO layer over a large area (Figure 2a)
Summary
Conventional liquid crystal (LC) electro-optical devices incorporate separate layers of a transparent electrode and an organic polymer film for driving devices and controlling LC alignment, respectively. The most common method to align LCs is by mechanical rubbing of a thin polymer film[1] coated on the surface of a transparent electrode. As alternatives to the rubbing process, noncontact methods such as photo-alignment[2,3,4,5] and ion-beam irradiation[6] have been used but they have critical drawbacks associated with controlling the orientation of photoswitchs on the surface and low anchoring energies.[7]. All of these ITO patterning methods do not achieve uniform high resolution and aspect ratio patterns over large areas without significant loss of electrical conductivity and optical transmittance, factors that are directly related to anchoring energies of LCs and energy efficiencies of devices
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