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US 6,784,955 B2Granted
Optically optimized permanently bistable twisted nematic liquid crystal displays
AssigneeThe Hong Kong University of Science and Technology
InventorsHoi-Sing Kwok, Jian-Xin Guo
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Abstract
The structure and construction of a bistable twisted nematic liquid crystal display with very long lifetime are disclosed. The two stable twist states in this display when no voltage is applied have almost infinite lifetimes and do not decay. These two stable twist states differ by a twist angle of 180°. New design conditions of this bistable twist structure are disclosed such that the contrast and the brightness are both optimized. This display can be operated in transmittive mode with two polarizes or in the reflective mode with one polarizer.
Claims4
A liquid crystal display comprising
- a) liquid crystal cell having top and bottom alignment layers with rubbing directions between them that favor a twist angle of ±22±5° to define a first stable state;
- b) an input polarizer with an angle of ±45±5° relative to the rubbing direction of an adjacent alignment layer and an output polarizer at an angle of ±68±5° relative to said rubbing direction;
- and
- c) a chiral dopant added to the liquid crystal layer of the liquid crystal cell such that a ratio of a thickness of the liquid crystal layer and a pitch of the liquid crystal twist is between 0.19±0.1 to define a second stable state;
- d) the thickness times birefringence of the liquid cell is 0.27±0.1 μm.
2 more elements
Dependencies are inferred from the claim text.