Why can surface-stabilized ferroelectric liquid crystal displays switch faster than nematic displays?
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
Surface-stabilized ferroelectric liquid crystal (SSFLC) displays switch faster than nematic displays because of their unique molecular structure and the nature of their response to an electric field.1
In an SSFLC device, the liquid crystal molecules possess a permanent charge separation, or ferroelectric dipole, which is a consequence of their optical activity and molecular tilt. This dipole is directly coupled to the tilt direction of the molecules. When an external voltage of the correct sign is applied, it interacts directly with this permanent dipole, allowing the molecules to reverse their tilt direction in tens of microseconds.1
In contrast, standard twisted-nematic displays rely on the alignment of liquid crystal directors with an applied electric field to change the polarization of light. This process is generally slower than the direct dipole-driven switching mechanism found in smectic SSFLC devices.21