Vertical alignment (VA) technologies for LCD
VA LCD technology increases transmission to give display screens incredible contrast.
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.
VA switching mode
In VA LC displays, the rod-shaped liquid crystals are almost vertically aligned between the glass plates in the off state (left). When voltage is applied (right), the molecules align themselves parallel to the glass plates.