Transcript Introduction to Liquid Crystal ECE-E443

Liquid Crystal Technology Overview
ECE-E443
Kai Chung Wong
Introduction

The study of liquid crystals began in 1888 when an
Austrian botanist named Friedrich Reinitzer observed
that a material known as cholesteryl benzoate had two
distinct melting points.

He increased the temperature of a solid sample and
watched the crystal change into a hazy liquid
Liquid Crystal
Characteristic
•Organic substance in the state between
solid and Liquid state
•Temperature between Tm and Tc
•Thin and Elongated structure
•Strong dipoles or easily polarizable
substituents
Dielectric anisotropy Property

Positive dielectric anisotropy
 Molecules

Negative dielectric anisotropy
 Molecules


will align parallel with electric field
will align perpendicular with electric field
The index of refraction is larger along with the
long axis of the molecules
Anisotropies of LC enable the index of refraction
to be controlled electrically
Anisotropy: Dielectric Constant
positive
++
+++
E
e
- ---
De = e - e
e
>0
E
negative
De = e - e < 0
E
all angles in
the plane 
to E are
possible for the
-De materials
Twisted Nematic LC
•Twisted nematic liquid crystal acts as a polarization
rotator, with polarization plane rotating in alignment
with the molecular twist.
Twisted Nematic LC Display



liquid crystal place
between two polarizer
Alignment layer force
molecules orientate in
the direction of the
polarization plane
Light follows the helix
shaped molecules
Passive matrix LCD
Super Twisted Nematic Displays
TFT Active Matrix LCD
Applications
LC Display
 Sensor

 Temperature
 Pressure
 Chemical

WDM
Questions?
Order Parameter