Ferro Liquid Display

Ferro Liquid Display or Ferro Liquid Crystal Displays (FLCD) is a display technology based on the ferroelectric properties of certain smectic liquid crystals.

Used in LCoS the dot pitch of such displays can be as low as 8 µm giving a very dense high resolution display on a small area. These find applications in 3D displays and head mounted displays (HMD) where typical LCDs have failed to provide anything better than a 640x480 (RGB pixel) resolution on a sq.cm display area.

Ferroelectric LCoS find commercial use also in Structured illumination in 3D-Metrology and Super-resolution microscopy.

To produce color, time multiplexing is used, exploiting the sub-millisecond switching time.

Working of Ferro Electric Crystals

FLCDs are smectic liquid crystals that have a layered order. Most FLCDs are

• of the smectic C phase (SmC^*)
  • i.e., they are tilted away from the layer normal (90°) and
• possess a chiral behaviour
  • i.e., they have a layered structure with the molecules at some angle (the "cone angle") away from the layer normal, and there is some inherent twist in the structure.

So, in an unconstrained system, the azimuthal direction in which the molecules tilt away from the layer normal will differ slightly from one layer to the next.

Typically, the FLCDs are built with cell gaps less than 2 µm for stable molecular alignment. Alignment layer causes perpendicular stacked alignment. The cell's polarisation is determined by the electric field applied. That in turn results in opaque or transparent layer when used in combination with polarised layers as in LCD.

Properties and uses

• Very thin layer (less than 2 µm thick) produce a 90° polarisation twist.
• High density LCoS displays with small display areas can be produced.
• Switching time is less than 100 µs
  • High frame rate video displays are possible.
• Magnetic polarisation effect is bistable.
  • Can be used for low frame rate displays that can run on very low power
  • This property can help build display with non-volatile memory with the advantage that the memory can be changed easily.
• Viewing angle is greater than 120°
  • This makes it suitable for commercial TV applications.

Some commercial products utilize FLCD.^[1][2]

High switching allows building optical switches and shutters in printer heads.^[3]

References