Electro-optic displays with reduced remnant voltage

Abstract

The invention provides materials and methods (including driving methods) for reducing the effects of remnant voltages in electro-optic displays.

1 . An electro-optic display comprising a layer of electro-optic material and voltage supply means for applying a voltage not greater than a predetermined value in either direction across the layer of electro-optic material, wherein the electro-optic material has a threshold voltage which is greater than zero but less than about one third of the predetermined value. 
     
     
         2 . An electro-optic display according to  claim 1  wherein the electro-optic material has a threshold voltage which is not less than about one-fiftieth but less than about one third of the predetermined value. 
     
     
         3 . An electro-optic display according to  claim 2  wherein the electro-optic material comprises a particle-based electrophoretic material comprising a suspending fluid and a plurality of electrically charged particles held in the suspending fluid and capable of moving therethrough on application of a voltage across the layer of electro-optic material. 
     
     
         4 . An electro-optic display according to  claim 3  wherein the electrophoretic material is an encapsulated electrophoretic material, a polymer-dispersed electrophoretic material or a microcell electrophoretic material. 
     
     
         5 . An electro-optic display according to  claim 3  wherein the suspending fluid is gaseous. 
     
     
         6 . An electrophoretic medium comprising a suspending fluid, a plurality of a first type of electrically-charged particle held in the suspending fluid and capable of moving therethrough on application of an electric field to the electrophoretic medium, and a plurality of a second type of electrically-charged particle held in the suspending fluid and capable of moving therethrough on application of an electric field to the electrophoretic medium, the particles of the second type having a charge of an opposite polarity to the particles of the first type, wherein the total charge on the particles of the second type is from about one-half to about twice the total charge on the particles of the first type. 
     
     
         7 . An electrophoretic medium according to  claim 6  which is an encapsulated electrophoretic medium, a polymer-dispersed electrophoretic medium or a microcell electrophoretic medium. 
     
     
         8 . An electrophoretic medium according to  claim 6  wherein the suspending fluid is gaseous. 
     
     
         9 . An electrophoretic medium according to  claim 6  which displays a remnant voltage of less than about 1 Volt one second after the application thereto of a square wave addressing pulse of 15 Volts for 300 milliseconds. 
     
     
         10 . An electrophoretic medium according to  claim 9  which displays a remnant voltage of less than about 0.2 Volt one second after the application thereto of a square wave addressing pulse of 15 Volts for 300 milliseconds. 
     
     
         11 . An electrophoretic medium comprising a suspending fluid, a plurality of a first type of electrically-charged particle held in the suspending fluid and capable of moving therethrough on application of an electric field to the electrophoretic medium, and a plurality of a second type of electrically-charged particle held in the suspending fluid and capable of moving therethrough on application of an electric field to the electrophoretic medium, the particles of the second type having a charge of an opposite polarity to the particles of the first type, the medium displaying a remnant voltage of less than about 1 Volt one second after the application thereto of a square wave addressing pulse of 15 Volts for 300 milliseconds. 
     
     
         12 . An electrophoretic medium according to  claim 11  which displays a remnant voltage of less than about 0.2 Volt one second after the application thereto of a square wave addressing pulse of 15 Volts for 300 milliseconds. 
     
     
         13 . An electrophoretic medium comprising a plurality of discrete droplets of a suspending fluid dispersed in a continuous phase, the droplets further comprising a plurality of electrically-charged particles held in the suspending fluid and capable of moving therethrough on application of an electric field to the electrophoretic medium, wherein the continuous phase has a volume resistivity not greater than about one-half of the volume resistivity of the droplets, and that both the continuous phase and the droplets having a volume resistivity of less than about 10 11  ohm cm.