Nematic liquid-crystal displays: Some properties and limitations

The objectives of this study were to determine the feasibility of utilizing nematic liquid crystals (LC) as media for aircraft displays from the point of view of their temperature range, response time, gray scale, and color control. According to this objective, the dynamic scattering and tunable birefringence mode of operation were investigated in some detail. Experiments, in agreement with derived mathematical models, led to the following conclusions : 1) The nematic temperature range can be made to fit any reasonable specification by forming multiple eutectic mixtures, provided the ingredients are compatible. 2) "Write" or "contact" times less than 2 µs have been (and less than 0.1 probably can be) realized with the help of "blocking" diodes. However, true rise times become generally longer than 1 s at temperatures below -20° C and electric fields at or below 3 V/µm. 3) The optical properties of electricallyinduced (dynamic) scattering can, in a first order approximation, be described by specifying the liquid crystal birefringence ratio
n_{0}/n_{e}
their average refractive index
\bar{n}
, and the applied voltage. 4) Of several possible color display approaches, electrically tunable birefringence was selected as the most promising one. The widest viewing angle, |α| ≤30°, is achieved with reflective displays and best color definition (resolution Δλ/λ≃0.2) with retardations of Γ≃3/2 in "single stage" displays, as long as the overall cell thickness fluctuation
\Delta d < 0.1 \lambda/(n_{e}-n_{0})
. In addition, nematic liquid scattering and color display features are compared to those of PLZT, an electrooptic ceramic.