FLCD - Ferroelectric Liquid Crystal Display ppt

1. FERROELECTRIC LIQUID
CRYSTAL DISPLAYS (FLCD)
Visit www.seminarlinks.blogspot.com to download

2. Introduction
FLCD, is a next generation display device that uses
the interactions between spontaneous
polarization of the ferrodielectric liquid crystal
and the electric field and provides rapid response
characteristics.

3. Ferrofluid
• A ferrofluid is a liquid which becomes
strongly magnetized in the presence of
a magnetic field.
• Ferrofluids are colloidal liquids made
of nanoscale ferromagnetic, or
ferrimagnetic, particles suspended in a
carrier fluid (usually an organic solvent
or water).

4. Advantages over traditional LCDs
Traditional LCDs
• Traditional LCD displays are usually of
the Super Twisted Nematic (STN)
variety.
• Response time in tens of miliseconds
(ms)
• Causes video anomalies
• Narrow visual angle
• Generates cross-talk among pixels
within a certain distance
• Lead to difficulties in reducing a pixel
size below a certain size.
FLCD
• Spontaneous polarization of the
ferrodielectric liquid crystal and the
electric field .
• provides rapid response characteristics
below 1 ms.
• Rapid response is essential to eliminating
video anomalies.
• Very wide viewing angles
• Can implement a high resolution with a
more reduced pixel size .
• Prevent cross-talk from occurring due to
strong interactions between molecules

5. The graphic, provided by Displaytech, nicely illustrates the comparison between
images produced by their FLC with VLSI backplane devices and the typical
AMLCD device.
Notice that the FLC device (left) allows full color on each pixel while each pixel
has only one color for the AMLCD device (right).

6. Working of Ferro Electric Crystals
• 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.

7. Geometry of chiral smectic C phase

8. • 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.

9. FLCD Operating Principle
• An FLCD acts as a classical half-wave plate, one whose optic axis can be
reoriented by an applied field:
• If the optic axis is parallel or perpendicular to incoming polarized light, the light passes
through the FLCD unchanged and is blocked by the exit polarizer(oriented at 90o to the
entrance polarizer)
• If the optic axis makes an angle of 45o to the incoming polarized light, the direction of
polarization changes by 90o and is able to pass through the exit polarizer
• Orientation of FLF molecules is changed by applying a
voltage pulse of suitable polarity.

10. FLCD Operation
Exit Polarizer
Glass
LC Molecule
(Rotates through
an angle of 45O)
Glass
Entrance Polarizer
Optical
Axis
Cell Spacing
OFF State ON State
DARK BRIGHT

11. FLCD Operation
• In thin FLC cells, a bistability appears with
two bistable states as shown in Fig.
• Ferroelectric liquid crystals have a
spontaneous polarization (Ps) whose
direction is perpendicular to the layer.
• When the electric field is applied,
molecules re-align in a way that the
direction of the spontaneous polarizations
is the same as that of the electric field.
• Combining a pair of polarizers (polarizer
and analyzer), FLCDs can realize dark and
bright states.
Principle of FLCD

12. Molecular orientation control
• It is one of the most important key technologies for the development
of practical FLCDs.
• The molecular orientations of FLCDs are classified as two layer
structures:
Bookshelf Layer
Chevron Layer

13. Molecular Orientation Control
• The FLC cells with parallel rubbing, in which the rubbing directions
of both substrates are the same, have been known to show four
orientational states with a chevron layer structure -
• C1-uniform (C1U), C1-twisted (C1T), C2-uniform (C2U) and C2-
twisted (C2T).
• Among them, the C1U and C2U orientations are useful for practical
applications because of their extinction positions between cross
nicols.

14. The C2U orientation

15. Device Structure

16. • On a color filter substrate and a
glass substrate with ITO electrodes
there are an insulating film and an
aligning films coated.
• The material of the aligning film was
polyimide.
• The rubbing direction of both
substrates is in the same direction
(parallel rubbing).
• An aligning film with a medium
pretilt angle (about 3°) was utilized
in order to gain 100% of the C2U
state without any zigzag defects or
any C1 states.

17. • Each pixel is divided into two areas with 1:2 ratio so as to realize
spatial dither gray scale.
• Spacer walls were constructed within the panel in order to show high
shock stability.
• The cell spacing was 1.3µm.
• Optimal adhesion between both substrates was obtained, yielding
higher shock stability more than 20kg/cm2.

18. 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.

19. Cont..
• Viewing angle is greater than 120°
 This makes it suitable for commercial TV applications.
• Some commercial products do seem to utilize FLCD.
• High switching allows building optical switches and shutters in printer
heads.

20. Flexible color moving-image FLC display (A4 size, 96×64 pixels, external-transistor-matrix driven)

21. Challenges
• The problems facing ferroelectric researchers are numerous.
• Alignment defect control (sensitive to shock and vibration)
• Cell spacing control
• Temperature range
• Response time, and Gray Scale
New fluorinated liquid crystal compounds are being developed to help
decrease the response time and improve the contrast ratio (contrast is
limited by defects).

22. Conclusion
• Prospects for the future are mixed for this technology.
• While much research continues, it is unclear what market the
ferroelectric LCD will serve.
• Certainly, if the problems can be solved, then the high contrast and
wide viewing angle achieved with ferroelectric LCDs will put them in
competition with active matrix LCDs.

23. References
• http://en.wikipedia.org/wiki/Ferro_Liquid_Display
• http://www.wtec.org/loyola/dsply_jp/c4_s7.htm
• http://www.google.co.in/patents/US6844909- Patent Ferrodielectric
liquid crystal display (FLCD) manufacturing method
• http://www-inst.eecs.berkeley.edu/~ee290d/sp99/ho17/sld022.htm
• http://plc.cwru.edu/tutorial/enhanced/files/flc/flcstruc/flcstruc.htm
Visit www.seminarlinks.blogspot.com to download