1. Liquid Crystal Technology Overview ECE-E443 Kai Chung Wong

2. 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

3. 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

4. Dielectric anisotropy Property Positive dielectric anisotropy  Molecules will align parallel with electric field Negative dielectric anisotropy  Molecules 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

5. Anisotropy: Dielectric Constant ++ + - - E    E  ++++++++ -------- positive negative all angles in the plane  to E are possible for the -  materials E

6. Twisted Nematic LC Twisted nematic liquid crystal acts as a polarization rotator, with polarization plane rotating in alignment with the molecular twist.

8. 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

9. Passive matrix LCD

10. Super Twisted Nematic Displays

12. TFT Active Matrix LCD

13. Applications LC Display Sensor  Temperature  Pressure  Chemical WDM

14. Questions?

15. Order Parameter