Methods for driving electrophoretic displays using dielectrophoretic forces

Abstract

A dielectrophoretic display has a substrate having walls defining a cavity, the cavity having a viewing surface and a side wall inclined to the viewing surface. A fluid is contained within the cavity; and a plurality of particles are present in the fluid. There is applied to the substrate an electric field effective to cause dielectrophoretic movement of the particles so that the particles occupy only a minor proportion of the viewing surface.

1 . A method for operating a dielectrophoretic display, the method comprising:
 providing a dielectrophoretic medium comprising a fluid and a plurality of at least one type of particle within the fluid;   applying to the medium an electric field having a high amplitude, low frequency component and a low amplitude high frequency component, thereby causing the particles to undergo electrophoretic motion and producing a first optical state; and   applying to the medium an electric field having a low amplitude low frequency component and a high amplitude high frequency component, thereby causing the particles to undergo dielectrophoretic motion and producing a second optical state different from the first optical state.   
     
     
         2 . A method according to  claim 1  wherein the low frequency components have frequencies not greater than about 10 Hz and the high frequency components have frequencies of at least about 100 Hz. 
     
     
         3 . A method according to  claim 1  wherein the components have substantially the form of square waves or sine waves. 
     
     
         4 . A method according to  claim 1  wherein the at least one type of particle is formed from an electrically conductive material. 
     
     
         5 . A method according to  claim 4  wherein the at least one type of particle is formed from a metal or carbon black. 
     
     
         6 . A method according to  claim 1  wherein the substrate comprises at least one capsule wall so that the dielectrophoretic display comprises at least one capsule. 
     
     
         7 . A method according to  claim 6  wherein the substrate comprises a plurality of capsules, the capsules being arranged in a single layer. 
     
     
         8 . A method according to  claim 1  wherein the substrate comprises a continuous phase surrounding a plurality of discrete droplets of the fluid having the at least one type of particle therein. 
     
     
         9 . A method according to  claim 1  wherein the substrate comprises a substantially rigid material having the at least one cavity formed therein, the substrate further comprising at least one cover member closing the at least one cavity.