Crystal clear

Researchers at the Georgia Institute of Technology have developed a new technique for creating vertical alignment among liquid crystal molecules which could lead to cheaper displays.

Manufacture of LCD panels is complex, requiring multiple steps that can introduce defects. Among the steps is the application of a polymer film, called the alignment layer, to the two pieces of glass between which the liquid crystals operate. The film, which must be rubbed after being coated on the glass, anchors the crystals with a fixed alignment. The process of rubbing to create the necessary alignment can damage some of the transistors and introduce dust, producing defects that can reduce the manufacturing yield of the panels.

By adding side chains to the polymer molecules, the researchers have found a way to eliminate the polymer rubbing step. Instead, they use the in-situ photopolymerisation of alkyl acrylate monomers in the presence of nematic liquid crystals. This provides a cellular matrix of liquid crystalline droplets in which the chemical structure of the encapsulating polymer controls the liquid crystal alignment.

Beyond simplifying the fabrication process and potentially increasing device yield, the technique also offers other advantages. Because devices are based on vertical alignment of the liquid crystals, their “off” state can be made completely dark. In addition, the liquid crystals provide strong binding between the two substrate surfaces. This makes the resulting display less sensitive to mechanical deformations and pressure, ideal for flexible displays that lack the structure provided by glass plates.