Bistable nematic liquid crystal display device with improved optical mask
AssigneeNemoptic
InventorsPhilippe Martinot-Lagarde, Alain Boissier, Jacques Angele, Bertrand Pecout, Ivan N Dozov
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Abstract
The invention relates to a bistable nematic liquid-crystal device comprising: alignment means, which orient the liquid crystal, means designed to apply electrical signals which allow switching, by breaking the anchoring on at least one of the two substrates, between two distinct textures, and means designed to promote the establishment of that one of the said textures giving the off state in the liquid crystal covering the inter-electrode spaces.
Claims34
Bistable nematic liquid-crystal display device with a liquid-crystal optical mask, characterized in that it comprises:
- a) a nematic liquid-crystal material contained between two parallel substrates, which are provided with electrodes on their facing inner surfaces in order to allow an electric field to be applied to the said liquid crystal, at least the front substrate and the front electrode being optically transparent;
- b) alignment layers or treatments on the electrodes which orient the liquid crystal and produce an alternation of at least two distinct textures that are stable or metastable in the absence of a field, where one of the textures is either not twisted or twisted through a total angle of between −90° and +90° and the other texture has an additional twist through an angle of about 180°;
- c) the thickness d of the liquid-crystal layer covering the electrodes being chosen so that the product d.Δn is close either to λ0/4 or λ0/2, to within an integer multiple of the wavelength, or else is between these two values, λ0 being the median wavelength of the useful spectral band of the display and Δn the birefringence of the liquid crystal for this wavelength;
- d) means designed to apply, to the liquid crystal covering the electrodes, electrical signals which allow it to switch, by breaking the anchoring on at least one of the two substrates, between the said distinct textures and allow it to remain in one of them after the field has been removed;
- and
- e) means designed to promote the establishment of that one of the said textures giving the off state in the liquid crystal covering the inter-electrode spaces.
Process for manufacturing a bistable nematic liquid-crystal display device with a liquid-crystal optical mask, characterized in that it comprises the steps consisting in:
- a) placing a nematic liquid-crystal material between two parallel substrates, which are provided with electrodes on their facing inner surfaces in order to allow an electric field to be applied to the said liquid crystal, at least the front substrate and the front electrode being optically transparent;
- b) forming alignment layers or treatments on the electrodes which orient the liquid crystal and produce an alternation of at least two distinct textures that are stable or metastable in the absence of a field, where one of the textures is either not twisted or twisted through a total angle of between −90° and +90° and the other texture has an additional twist through an angle of about 180°;
- c) controlling the thickness d of the liquid-crystal layer covering the electrodes so that the product d.Δn is close either to λ0/4 or λ0/2, or else is between these two values, λ0 being the median wavelength of the useful spectral band of the display and Δn the birefringence of the liquid crystal for this wavelength;
- d) providing means designed to apply, to the liquid crystal covering the electrodes, electrical signals which allow it to switch, by breaking the anchoring on at least one of the two substrates, between the said distinct textures and allow it to remain in one of them after the field has been removed;
- and
- e) providing means designed to promote the establishment of that one of the said textures giving the off state in the liquid crystal covering the inter-electrode spaces.
Dependencies are inferred from the claim text.