VERTICALLY ALIGNED NEMATIC LCDS

The vertically aligned nematic (VAN), which is also known as the electricallycontrolled birefringence (ECB) effect, was first described in 1971 but wasinferior to the twisted nematic effect. VAN LCDs require homeotropicalignment of the liquid crystal molecules at the glass surface (long axis isperpendicular to the surface) and a negative dielectric anisotropy. Bothconditions have been hard to achieve until recently. The principle of operationis based on a change in birefringence induced by tilting the molecules with anapplied field. A steep threshold characteristic can be achieved with carefulcontrol of the surface tilt angle and the cell spacing and by using liquid crystalswith specific elastic constants (high ratio of bend/splay elastic constants). Full-color VAN LCDs were demonstrated by Stanley Electric Company at the JapanElectronics Show.


30 August, 1995; WTEC Hyper-Librarian