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 which is perpendicular to the substrate. This requires liquid crystal mixtures with negative dielectric anisotropy which 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 LCD technology has been in commercial use since 1998. Our LCD Explorer visually demonstrates how a VA display works.
Varieties of VA technology are
The key to all varieties is to define the switching behavior in advance in order to speed up the switching time.