On the Electric Field Induced Stripe Instability Threshold of Twisted Nematic Layers

Soon after the production of twisted nematic (TN) liquid crystals by Schadt and Helfrich in 1971 [l], commercialization of low information content liquid crystal displays (LCDs) for watches and calculators began. However, passive matrix addressing of TN cells did not satisfy the requirements for contrast ratio and viewing angle in high information content displays in laptop computers. These problems could potentially be overcome by the introduction of the active matrix addressing (TFT technology) [2], but this is more expensive and suffered from only small yields. In 1985 the first prototype supertwisted nematic (STN) displays, driven by a passive matrix, were demonstrated by Scheffer, Nehring et al. [3]. These offered substantial improvements of viewing angle and contrast ratio over the high information content passive matrix TN displays. Commercialization of STN displays for laptop computers and wordprocessors started in 1987. Compensation techniques, necessary for producing colored displays with RGB filter technology, came into produc-tion by the end of the 1980s. Today the range of STN display applications spans from automotive uses, through mobile telephones, personal digital assistants (PDA) and wordprocessors to color displays in laptop computers and reflective color LCDs [4]. The disadvantages of STN LCDs are the low response speed, not suitable for video applications, and the limited viewing angle compared to TFT technology. There is strong competition from improved TFT displays [5-71 and prototypes of in-plane switching (IPS) [8, 91, vertically aligned TN (VAN-TN) [ 10, 1 11 and electrically controlled birefringence (ECB) modes offering video operation and minimum viewing angle dependence. However, STN displays are still cheaper in price and even though the costs for TFT displays have decreased there is still a price factor of about two between these technologies. It can be expected that STN displays will enter the monitor marked soon. At the Japan electronics show in 1996 several prototypes of 17.7 inch STN monitors were presented. The largest display prototype shown so far is a 21.4 inch XGA-format STN-LCD.

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Equilibrium structures of planar nematic and cholesteric films in electric fields

Schiller

1990

Phase Transitions

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On the Electric Field Induced Stripe Instability Threshold of Twisted Nematic Layers

Abstract: Based on continuum theory, general expressions are derived which indicate how the electric field induced stripe instability threshold of twisted nematic layers is influenced by the liquid crystal material parameters. Results are applied to supertwist displays.

Cited by 5 publications

References 9 publications

Applications, TN, STN Displays

Applications, TN, STN Displays

Nematic Liquid Crystals: Applications, Section 3.1

Equilibrium structures of planar nematic and cholesteric films in electric fields

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