Ferro Liquid Display
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Ferro Liquid Display, or Ferro-electric Liquid Display (FLD) or Ferro Fluid Display (FFD), is a display technology based on the ferroelectric properties of certain liquids. Not all such fluids are crystal but they are generically referred to as Ferro Liquid Crystal Displays (FLCD).
These fluids have bistable properties that can be switched with a magnetic field. The switching time is much shorter than that of a typical LCD that twist/untwist due to magnetic rather than electric interactions.
Also see Ferrofluid for how some liquids behave in presence of a magnetic field. Practically the switching time is just the same as the time it takes for the electric signal to switch (the magnetic field). The ferro liquid reacts almost instantly when used in µg quantities (thin layer) as in a typical LCD's crystal layer.
The dot pitch of such displays can be as low as 10 µm giving a very dense high resolution display on a small area. These might 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.
Displays based on these are still experimental or of less commercial value only due to the costs. Gradual adoption in consumer electronics is expected to bring the costs down.
A major drawback is that the angle of twist is not easily controlled by intensity of magnetic field. To produce color scales, time multiplexing might be used exploiting the quick switching time. The materials found so far are sensitive to vibration and shock.
Working of Ferro Electric Crystals
Those based on crystals can retain polarisation permanently. FLCDs are smectic liquid crystals that have a natural 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, 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 magnetic 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) can help produce a 90° polarisation twist.
- High density displays with small display areas can be produced.
- DisplayTECH claims that a stamp sized FLCD can drive resolutions needed for 50 inch screens.
- 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.