Multi-color electro-optic displays

Abstract

An electro-optic display comprising at least two separate layers of electro-optic material, with one of these layers being capable of displaying at least one optical state which cannot be displayed by the other layer. The display is driven by a single set of electrodes between which both layers are sandwiched, the two layers being controllable at least partially independently of one another. Another form of the invention uses three different types of particles within a single electrophoretic layer, with the three types of particles being arranged to shutter independently of one another.

1 . An electro-optic display comprising at least first and second layers of electro-optic material, the display further comprising a plurality of pixel electrodes disposed on one side of the first and second layers and defining a plurality of pixels of the display, and a single continuous second electrode disposed on the opposed side of the first and second layers from the first electrode and extending across all the pixels of the display, there being no electrode between the first and second layers. 
     
     
         2 . An electro-optic display according to  claim 1  further comprising a third layer of electro-optic material, the third layer being capable of displaying at least one optical state which cannot be displayed by the first and second layers, the second electrode being disposed on the opposed side of the first, second and third layers from the first electrode, there being no electrode between the second and third layers. 
     
     
         3 . An electro-optic display according to  claim 2  wherein the three layers contain cyan, magenta and yellow pigments, in any order. 
     
     
         4 . An electro-optic display according to  claim 3  wherein the layer containing the yellow pigment is arranged to have a smaller number of gray levels than the layers containing the cyan and magenta pigments. 
     
     
         5 . An electro-optic display according to  claim 3  having a viewing surface through which an observer views the display, and wherein the two electro-optic layers closest to the viewing surface contain cyan and yellow pigments, in either order. 
     
     
         6 . An electro-optic display according to  claim 1  wherein at least one of the layers of electro-optic material comprises an electrophoretic material comprising a plurality of charged pigment particles dispersed in a fluid and capable of moving through the fluid on application of an electrical field to the layer. 
     
     
         7 . An electro-optic display according to  claim 6  wherein at least one of the first and second layers comprises a microcavity electrophoretic material. 
     
     
         8 . An electro-optic display according to  claim 6  wherein the charged particles in at least one of the layers are movable between a first optical state, in which the pigment particles occupy substantially the whole area of each pixel, and a second optical state, in which the pigment particles occupy only a minor proportion of the area of each pixel. 
     
     
         9 . An electro-optic display according to  claim 8  wherein the charged particles in each of the first and second layers are movable between a first optical state, in which the pigment particles occupy substantially the whole area of each pixel, and a second optical state, in which the pigment particles occupy only a minor proportion of the area of each pixel. 
     
     
         10 . An electro-optic display according to  claim 9  wherein the yield stresses of the fluids in the first and second layers differ. 
     
     
         11 . An electro-optic display according to  claim 9  wherein the sizes of the microcavities in the first and second layers differ. 
     
     
         12 . An electro-optic display according to  claim 9  wherein the particles in the first and second layers differ in at least one of size, shape and electrical conductivity. 
     
     
         13 . An electro-optic display according to  claim 9  wherein the fluids in the first and second layers differ in at least one of viscosity and electrical conductivity. 
     
     
         14 . An electro-optic display according to  claim 9  having a viewing surface at or adjacent the surface of the first electro-optic layer remote from the second electro-optic layer, the electro-optic display further comprising a third electro-optic layer on the opposed side of the second electro-optic layer from the viewing surface, the third electro-optic layer comprising first and second types of particles of differing colors disposed in a fluid and capable of moving through the fluid on application of an electric field to the third electro-optic layer, the first and second types of particles being of differing electrophoretic mobility. 
     
     
         15 . An electro-optic display according to  claim 14  wherein the first type of particles in the third electro-optic layer are white. 
     
     
         16 . An electro-optic display according to  claim 15  wherein the particles in the first and second electro-optic layers are yellow and cyan, in either order, and the second type of particles in the third electro-optic layer are magenta. 
     
     
         17 . An electro-optic display according to  claim 1  wherein at least one of the first and second electrodes occupies only a minor proportion of the area of a pixel. 
     
     
         18 . An electro-optic display according to  claim 7  wherein the walls of the microcavity have a higher electrically conductivity than the phase comprising the plurality of charged pigment particles dispersed in the fluid. 
     
     
         19 . An electro-optic display according to  claim 1  wherein one of the electro-optic layers has at least two stable states, and the second electro-optic layer has only one stable state. 
     
     
         20 . A microcavity electrophoretic display comprising walls defining at least one cavity, the cavity containing a fluid and first, second and third types of particles dispersed in the fluid, each of the first, second and third types of particles having an unshuttered state, in which the particles occupy substantially the entire area of the microcavity, and a shuttered state, in which the particles occupy only a minor proportion of the areas of the microcavity, the first, second and third particles being of differing colors and differing in dielectrophoretic and/or electro-osmotic properties such that the first, second and third types of particles can be moved between their unshuttered and shuttered states independently of one another. 
     
     
         21 . A microcavity electrophoretic display according to  claim 20  wherein the colors of the first, second and third types of particles are such that when all three types of particles are in their unshuttered states the display appears substantially black.