Vertical alignment (VA) technologies for LCD
The ideal black screen
In VA (vertical alignment) LCDs, homeotropic liquid crystals – i.e. those aligned perpendicular to the substrate surface – are switched parallel to the glass substrate by the application of an electric field that is perpendicular to the substrate. This requires liquid crystal mixtures with negative dielectric anisotropy that are aligned perpendicular to the electric field. This is achieved by introducing lateral polar side groups to mesogenic molecules.
When no voltage is applied, the homeotropic orientation of the liquid crystals initially produces an almost ideal black state between crossed polarizers. VA displays are therefore characterized by excellent contrast values and are generally operated in normally black mode. This means that the screen is black when no voltage is applied.