Nam-Seok Lee

P-89: A Novel Dynamic Drive Scheme for Reflective Cholesteric Displays

We have developed a novel dynamic drive scheme for cholesteric LCD utilizing 3 and 2 levels driver ICs for row and column, respectively. Stable gray scale has also been accomplished by using a pulse position modulation. By adopting this new drive scheme, we have developed 5.7″ folder type VGA cholesteric LCD showing addressing speed of 1msec/line.

Improving the electro-optical properties of bistable reflective cholesteric liquid crystal displays

We have improved the electro‐optical properties of a bistable cholesteric liquid crystal display (Ch‐LCD) that is driven by a 3+2 dynamic driving scheme (3+2 DDS). The best contrast ratio is achieved at the selection period of 1.2–1.5 ms/line and the temperature range 26–30°C. The suitable preparation period and evolution period for contrast ratio are 40 times and 20 times the selection time, respectively. In the 3+2 DDS, rubbing the homeotropic alignment layer increases reflectivity of the ON state and keeps the reflectivity of the OFF state at the same level, so reflectivity and contrast ratio alike increase as a result. However, in a delayed homeotropic reset driving method, when the homeotropic alignment layer is rubbed, the reflectivity of both the ON and OFF states increases, thus the contrast ratio decreases. The combination of driving method and aligned surface morphology influences the relaxation mechanism in the cholesteric texture. By optimizing panel condition, we have demonstrated an 8.4″ foldable VGA Ch‐LCD that exhibits high reflectivity and contrast ratio with an addressing speed of around 1.2 ms/line.

P‐108: A Simple Matrix Driving of Bistable Liquid Crystal Displays

We have extended the basic idea of 2+2 dynamic driving scheme (DDS) to VGA (640×480) panel and optimized it to show the ON-OFF switching characteristic. The position dependence upon pre and post selection is serious and not suitable for driving the panel. We found that two steps of a propagation period provide the most stable homeotropic state and ON-OFF switching system. With this new driving scheme the potential gray scale for Ch-LCD in a 640×480 pixels matrix was examined.

16-2: A Novel S-PVA Cell Structure with High Contrast Ratio

This paper describes a new S-PVA cell structure which achieves enhanced contrast ratio by adopting a step-like patterned common electrode between the high sub-pixel and low sub-pixel electrodes without loss of transmittance. A 24-inch panel was developed for monitor applications and measured contrast ratio and white luminance were over 2500:1 and 400cd/m2, respectively.