Controlled gap states for liquid crystal displays
View Patent ↗The present invention relates to a bistable matrix-addressable display element comprising a substrate, a bistable electrically modulated imaging layer having a reflection maximum, at least one conductor, and at least one field-spreading layer between said bistable electrically modulated imaging layer and said at least one conductor, wherein said field-spreading layer has a sheet resistance (SER) of less than 10 9 Ohms per square and a method of imaging the display comprising identifying an area to be updated of said bistable matrix-addressable display element, wherein said area to be updated comprises rows of pixels; and applying a sequence of drive signals having a 4-phase approach to image said bistable matrix-addressable display element, which may be characterized as a planar reset, left-slope selection method.
1. A method of imaging a bistable matrix-addressable display element comprising:
providing a bistable matrix-addressable display element comprising a substrate, a bistable chiral nematic liquid crystal imaging layer having a reflection maximum, at least one conductor, and at least one field-spreading layer between said bistable chiral nematic liquid crystal imaging layer and said at least one conductor, wherein said field-spreading layer has a sheet resistance (SER) of from 10.sup.9 to 10.sup.6 Ohms per square;
identifying an area to be updated of said bistable matrix-addressable display element, wherein said area to be updated comprises rows of pixels; and
applying a sequence of drive signals having a 4-phase approach to image said bistable matrix-addressable display element, wherein said 4-phase approach comprises:
in phase 1, applying a first pixel voltage across said pixels of said area to be updated such that the critical voltage is reached; and holding said first pixel voltage until a homeotropic texture is reached;
in phase 2, setting a second pixel voltage to allow said homeotropic texture to relax into a stable planar texture;
in phase 3, selecting one row of pixels of said rows of pixels of said area to be updated; and updating said one row of pixels by addressing, wherein addressing comprises
applying a third pixel voltage, capable of switching said pixels from said stable planar texture to said non-reflective focal conic texture, across said pixels to produce switched pixels;
applying a fourth pixel voltage, incapable of switching said pixels from said stable planar texture to said non-reflective focal conic texture, to produce unswitched pixels to remain in the stable planar texture; and
repeating said addressing until said rows of pixels of said area to be updated have been addressed; and
in phase 4, removing said first pixel voltage, said second pixel voltage, said third pixel voltage, and said fourth pixel voltage from said area of said bistable matrix-addressable display element to be updated.
2. The method of claim 1 wherein said first pixel voltage, said second pixel voltage, said third pixel voltage, and said fourth pixel voltage comprise AC voltages.
3. The method of claim 1 wherein said addressing is sequential.
4. The method of claim 1 wherein at least one of said first pixel voltage, said second pixel voltage, said third pixel voltage, and said fourth pixel voltage is a voltage pulse.
5. The method of claim 1 wherein said bistable chiral nematic liquid crystal imaging layer comprises a polymer dispersed bistable chiral nematic liquid crystal imaging layer.