Patent Publication Number: US-2018031941-A1

Title: Multi-electrode total internal reflection image display

Description:
This application claims the filing date benefit of U.S. Provisional Application No. 62/115,361, filed on Feb. 12, 2015, the entirety of which is incorporated herein by reference. 
    
    
     FIELD 
     The instant disclosure is directed to a method and apparatus for total internal reflection-based image displays. Specifically, an embodiment of the disclosure relates to reflective image displays capable of displaying images composed of at least three different color states with a multi-electrode design. 
     Light modulation in conventional single particle total internal reflection (TIR) image displays are controlled by movement of a plurality of light absorbing electrophoretically mobile particles into and out of the evanescent wave region at the surface of the front sheet comprising of convex protrusions under an applied voltage across the electrophoretic medium. The particles may have either a positive or negative charge with a single optical characteristic. A first optical state of the display may be formed when the particles are attracted to the evanescent wave region where incident light rays are absorbed by the mobile particles (referred to as the dark state). A second optical state may be displayed when the particles are moved out of the evanescent wave region towards a rear electrode where light rays may be totally internally reflected to form a light or bright state. 
     This application describes a two-particle TIR image display comprising a plurality of particles of opposite charge polarity and different optical characteristics capable of forming at least three different optical states. TIR may be frustrated to create light absorbing or dark states by application of a voltage bias and moving either the plurality of positively or plurality of negatively charged particles into the evanescent wave region. A third optical state may be formed by moving both pluralities of particles out of the evanescent wave region. This disclosure further describes multi-electrode display architectures. The combination of particles of opposite charge polarity and different optical characteristics in combination with multi-electrode display architectures leads to TIR image displays capable of displaying images with multiple colors that is described herein. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other embodiments of the disclosure will be discussed with reference to the following exemplary and non-limiting illustrations, in which like elements are numbered similarly, and where: 
         FIG. 1A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a first optical state according to one embodiment of the disclosure; 
         FIG. 1B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a second optical state according to one embodiment of the disclosure; 
         FIG. 1C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a third optical state according to one embodiment of the disclosure; 
         FIG. 2A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a first optical state according to one embodiment of the disclosure; 
         FIG. 2B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a second optical state according to one embodiment of the disclosure; 
         FIG. 2C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a third optical state according to one embodiment of the disclosure; 
         FIG. 3A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a first optical state according to one embodiment of the disclosure; 
         FIG. 3B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a second optical state according to one embodiment of the disclosure; 
         FIG. 3C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a third optical state according to one embodiment of the disclosure; and 
         FIG. 4  schematically illustrates an exemplary system for implementing an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments provided herein describes total internal reflection-based image displays capable of displaying at least three different colors. In an exemplary embodiment, the disclosure provides a total internal reflection-based image display comprising a first and second plurality of electrophoretically mobile particles of different charge polarity and color and three electrodes that may be independently controlled. When the first plurality of particles may be moved into the evanescent wave region a first color may be exhibited. When the second plurality of particles may be moved into the evanescent wave region a second color may be exhibited. When both the first and second plurality of particles are moved out of the evanescent wave region, a third color may be exhibited. 
       FIG. 1A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a first optical state according to one embodiment of the disclosure. Display  100  in  FIG. 1A  comprises a transparent front sheet  102  containing a plurality of partially embedded high refractive index transparent hemispherical beads  104  in the inward surface, a grounded transparent front electrode layer  106  on the surface of the hemispherical beads and a rear support  108 . Rear support  108  may be further equipped with two rear electrodes  110  and  112  such as in a thin film transistor or patterned electrode array and a voltage source (not shown) that connects the front and rear electrodes. 
     Alternatively, transparent front sheet  102  may define a continuous, high refractive index transparent sheet with convex protrusions. The convex protrusions may be in the shape of hemispherical protrusions as illustrated in  FIG. 1A . Front sheet  102  may comprise a polymer such as polycarbonate. Front electrode  106  may comprise a transparent conductive material such as indium tin oxide (ITO), Baytron™, conductive nanoparticles, metal, nanowires, graphene or other conductive carbon allotropes or a combination of these materials dispersed in a substantially transparent polymer. 
     Rear electrode  110 ,  112  may comprise a conductive material such as indium tin oxide (ITO), conductive particles, metal nanowires, Baytron™, graphene or other conductive carbon allotropes or a combination thereof dispersed in a polymer or a metallic-based conductive material (e.g., aluminum, gold or silver). Rear electrodes  110 ,  112  may comprise one or more of a thin film transistor (TFT) array, direct drive patterned array of electrodes or a passive matrix array of electrodes. 
     Contained within the cavity formed by the front electrode  106  and rear electrodes  110 ,  112  may be an inert, low refractive index air or fluid medium  114 . Medium  114  may be a hydrocarbon. In an exemplary embodiment, medium  114  may be a fluorinated hydrocarbon or a perfluorinated hydrocarbon. In an exemplary embodiment, medium  322  may be Fluorinert™ perfluorinated hydrocarbon liquid available from 3M, St. Paul, Minn. 
     Medium  114  may further include a plurality of suspended light absorbing electrophoretically mobile particles  116 ,  118 . In an exemplary embodiment, medium  114  has a lower refractive index than front sheet  102 . The cavity formed between front electrode  106  and rear electrodes  110 ,  112  may further comprise spacer units (not shown) such as beads to control the size of the gap between the front and rear electrodes. The spacer units may comprise glass, metal or an organic polymer. 
     Mobile particles  116  comprise a first charge polarity and first optical characteristic (i.e. color). Mobile particles  118  comprise a second charge of opposite polarity and a second optical characteristic. Particles  116  or  118  may be any color of the visible spectrum or a combination of colors to give a specific shade or hue. Particles  116 ,  118  may be formed of an organic material or an inorganic material or a combination of an organic and inorganic material. Particles  116 ,  118  may be a dye or a pigment or a combination thereof. Particles  116 ,  118  may be at least one of carbon black, a metal or metal oxide. The particles may have a polymer coating. In one embodiment, particles  116  illustrated in display  100  in  FIG. 1A  may consist of a positive charge polarity while particles  118  consist of a negative charge polarity. 
     The exemplary embodiment of display  100  further includes an optional dielectric layer  120  located on the surface of transparent front electrode  106  and disposed between transparent front electrode  106  and medium  114 .  FIG. 1A  illustrates a dielectric layer  122  on the surface of the rear electrodes  110 ,  112  in display  100  such that dielectric layer  122  is disposed between the rear electrodes  110 ,  112  and medium  114 . Having a dielectric layer on the rear electrode may be optional and may depend on the composition of the rear electrode. The dielectric layers may be used to protect one or both of the front electrode layer  106  and rear electrode layers  110 ,  112 . The dielectric layers may be substantially uniform, continuous and defect-free layer of as least about 20 nanometers in thickness. Dielectric compounds may be organic or inorganic in type. The most common inorganic dielectric material is silicon dioxide commonly used in integrated chips. Organic dielectric materials are typically polymers such as polyimides, fluoropolymers, polynorbornenes and hydrocarbon-based polymers lacking polar groups. In an exemplary embodiment, the dielectric layers comprise parylene. In another embodiment the dielectric layers comprises a halogenated parylene. Other inorganic or organic dielectric materials or combinations thereof may also be used for the dielectric layers. 
     The dielectric layers may each have a thickness of at least 80 nanometers. In an exemplary embodiment, the thickness is about 80-200 nanometers. Advantageously, parylene has a low dielectric constant and may be made as thin as 20 nanometers without having pinhole leakage paths. Such features contribute to display structures having a comparatively high capacitance per unit area. The high capacitance means that the required number per unit area of charged mobile particles may be attracted to the parylene at a lower voltage than if the thickness was higher or if the dielectric constant was lower. 
     Referring again to  FIG. 1A , display  100  illustrates a pixel of the display in a first optical state. The optical state may be created by absorption of incident light rays by negatively charged particles  118  of a first optical characteristic. In this state, the electrophoretically mobile positively charged particles  116  may be moved under the influence of an applied voltage bias towards rear electrode surfaces  110 ,  112 . In the example in  FIG. 1A , rear electrodes  110 ,  112  have an applied voltage bias V 1  and V 2 , respectively, of −5V (It should be noted that other voltage biases of varying magnitudes may be applied as −5V is used for illustrative purposes only). The negatively charged particles  118  may be moved near the front dielectric layer adjacent the grounded front electrode surface  106  that has a +5V bias (V G ) into the evanescent wave region such that TIR is frustrated and incident light rays are absorbed. This is illustrated by incident light rays  124  and  126  that may be absorbed by the negatively charged particles  118  whereby the portion of the display in  FIG. 1A  observed by viewer  128  exhibits the optical characteristic (i.e. color) of the negatively charged particles  118 . 
       FIG. 1B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a second optical state according to one embodiment of the disclosure. Display  100  in  FIG. 1B  is the same as that described in  FIG. 1A  in the preceding paragraphs but illustrates how a second optical state may be formed. Display  100  in  FIG. 1B  illustrates a pixel of the display in a second optical state created by absorption of incident light rays by positively charged particles  116  having a second optical characteristic. In this state, electrophorectically mobile particles  118  with a negative charge polarity may be moved under the influence of an applied voltage bias near dielectric layer  120  adjacent to rear electrode surfaces  110 ,  112 . In this example in  FIG. 1B , the rear electrodes  110 ,  112  have an applied voltage bias V 1  and V 2 , respectively, of +5V (It should be noted that other voltage biases of varying magnitudes may be applied as +5V is used for illustrative purposes only). Particles  116  of a positive charge polarity are moved near the front dielectric layer adjacent the grounded front electrode surface  106  that has a −5V bias (V G ) and into the evanescent wave region. When the particles enter the evanescent wave region and frustrate TIR, the incident light rays may be absorbed. This is illustrated by incident light rays  130  and  132  that may be absorbed by the positively charged particles  116 . Thus the portion of the display in  FIG. 1B  observed by viewer  128  may exhibit the optical characteristic (i.e. color) of the positively charged particles  116 . 
       FIG. 1C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and three electrodes in a third optical state according to one embodiment of the disclosure. Display  100  in  FIG. 1C  is the same as that described in  FIGS. 1A-B  in the preceding paragraphs but illustrates how a third optical state may be formed. In this state, mobile particles  116  with a positive charge polarity may be moved under the influence of an applied voltage bias, V 2 , of −5V towards rear electrode  112 . The mobile particles  118  with a negative charge polarity may be moved under the influence of an applied voltage bias, V 1 , of +5V towards rear electrode  110 . In this state of the display in  FIG. 1C , there may be no particles in the evanescent wave region near grounded front electrode  106  which has a voltage bias, V G , of 0V. Incident light rays  134  and  136  may be instead totally internally reflected back towards viewer  128  as reflected light rays  138  and  140 , respectively, to create a light or bright state. This forms a third optical state of the display. 
       FIG. 2A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a first optical state according to one embodiment of the disclosure. Display  200  in  FIG. 2A  is similar to display  100  in  FIGS. 1A-C  explained in preceding paragraphs but with some differences in the design of the rear electrodes. Display  100  has a first and second electrode in each pixel. Display  200  in  FIG. 2A  is of a pixel with an array of more than two interdigitated electrodes  240 ,  242 . In an exemplary embodiment electrodes  240 ,  242  may be arrayed in an alternating fashion. In  FIGS. 2A-C  rear electrode  242  is highlighted by cross hatches to distinguish from adjacent electrodes  240 . In other embodiments electrodes  240 ,  242  may be arranged in any periodic manner. Electrodes  240 ,  242  may be further supported by a rear support  208 . A first plurality of electrodes  240  may be controlled by a first transistor and a second plurality of electrodes  242  may be controlled by a second transistor. Each plurality of electrodes  240  or  242  may consist of at least two electrodes. Ideally the width of electrodes  240 ,  242  would decrease as the number of electrodes increases per each pixel while keeping the dimensions of the pixel constant. 
     Multiple electrodes within each pixel may provide an additional advantageous feature of the display design in  FIG. 2A . Multiple electrodes may lead to decreased lateral electric fields within the cavity containing medium  214  and mobile particles  216 ,  218 . Reducing the lateral electric fields may reduce lateral movement and migration oi the particles. This may lead to a more uniform display performance. The cavity formed between the front dielectric layer  206  and rear dielectric layer  222  and rear electrodes  240 ,  242  in  FIG. 2A  may further comprise spacer units (not shown) such as beads to control the size of the gap between the front and rear electrodes. 
     The exemplary embodiment of display  200  may further include an optional dielectric layer  220  located on the surface of transparent front electrode  206  and disposed between transparent front electrode  206  and medium  214 . Front electrode  206  is located on the inward side of transparent front sheet  202  where the plurality of protrusions  204  exists.  FIG. 2A  illustrates a dielectric layer  222  on the surface of the rear electrodes  240 ,  242  in display  200  such that the dielectric layer is disposed between the rear electrodes  240 ,  242  and medium  214 . Having a dielectric layer on the rear electrodes may also be optional and may depend on the composition of the rear electrodes. The dielectric layers may each be a uniform layer of at least about 20 nanometers in thickness. Dielectric compounds may be organic or inorganic in type. The most common inorganic dielectric material silicon dioxide commonly used in integrated chips. Organic dielectric materials are typically polymers such as polyimides, fluoropolymers, polynorbornenes and hydrocarbon-based polymers lacking polar groups. In an exemplary embodiment, the dielectric layers comprise parylene. In another embodiment the dielectric layer comprises halogenated parylene. Other inorganic or organic dielectric materials or combinations thereof may also be used. 
     The dielectric layer may have a thickness of at least 80 nanometers. In an exemplary embodiment, the thickness is about 80-200 nanometers. Advantageously, parylene has a low dielectric constant and may be made as thin as 20 nanometers without having pinhole leakage paths. Such features contribute to display structures having a comparatively high capacitance per unit area. The high capacitance means that the required number per unit area of charged mobile particles may be attracted to the parylene at a lower voltage than if the thickness was higher or if the dielectric constant was lower. 
     Referring again to  FIG. 2A , display  200  illustrates a pixel of the display in a first optical state. The optical state may be created by absorption of incident light rays by the particles  218  with a negative charge polarity and a first optical characteristic. In this state, the electrophoretically mobile particles  216  with a positive charge polarity may be moved under the influence of an applied voltage bias near the plurality of rear electrodes  240 ,  242 . The plurality of electrode  240  and  242  may be interdigitated but it is not required for operation of display  200 . In the example in  FIG. 2A , the rear electrodes  240 ,  242  may have an applied voltage bias V 1  and V 2 , respectively, of −5V (It should be noted that other voltage biases of varying magnitudes may be applied as −5V is used for illustrative purposes only). The negatively charged particles  218  may be moved near the front electrode surface  206  that has a +5V bias (V G ) into the evanescent wave region such that TIR is frustrated and incident light rays may be absorbed. This is illustrated by incident light rays  244  and  246  that are absorbed by the negatively charged particles  218 . Thus the portion of the display in  FIG. 2A  observed by viewer  228  exhibits the optical characteristic (i.e. color) of the particles  218  with a negative charge polarity. 
       FIG. 2B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a second optical state according to one embodiment of the disclosure. Display  200  in  FIG. 2B  is the same as that described in  FIG. 2A  in the preceding paragraphs but illustrates a second optical state. Display  200  in  FIG. 2B  illustrates a pixel of the display in a second optical state created by absorption of incident light rays by particles  216  with a positive charge polarity and a second optical characteristic. In this state, the electrophoretically mobile particles  218  with a negative charge polarity have been moved under the influence of an applied voltage bias towards rear electrodes  240 ,  242 . In the example in  FIG. 2B , rear electrodes  240 ,  242  have an applied voltage bias V 1  and V 2 , respectively, of +5V (It should be noted that other voltage biases of varying magnitudes may be applied as +5V is used for illustrative purposes only). The positively charged particles  216  may be moved near the evanescent wave region adjacent the grounded front electrode surface  206  that has a −5V bias (V G ). In this position, particles  216  may frustrate TIR and absorb incident light rays. This is illustrated by incident light rays  248  and  250  in  FIG. 2B  that are absorbed by the positively charged particles  216 . Thus the portion of the display in  FIG. 2B  observed by viewer  228  exhibits the optical characteristic (i.e. color) of the particles  216  with a positive charge polarity. 
       FIG. 2C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles and interdigitated rear electrodes in a third optical state according to one embodiment of the disclosure. Display  200  in  FIG. 2C  is the same as that described in  FIGS. 2A-B  in the preceding paragraphs but exhibits a third optical state. In this state, the mobile positively charged particles  216  may be moved under the influence of an applied voltage bias, V 1 , of −5V near rear electrode  240 . The mobile negatively charged particles  218  have be moved under the influence of an applied voltage bias, V 2 , of +5V near rear electrode  242 . In this state of the display in  FIG. 2C  there may be no particles in the evanescent wave region near the grounded front electrode  206  which has a voltage bias, V G , of 0V. Incident light rays  252  and  254  may instead be totally internally reflected back towards viewer  228  as reflected light rays  256  and  258 , respectively, to create a light or bright state. This is a third optical state of the display. 
       FIG. 3A  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a first optical state according to one embodiment of the disclosure. Display  300  in  FIG. 3A  is similar to displays  100  and  200  explained in preceding paragraphs but with differences in the design of the rear electrodes. Display  100  has a first and second electrode in each pixel. Display  200  contains a plurality of more than two electrodes each of  240  and  242  in a single pixel in an array. Display  300  may also consist of a plurality of at least two electrodes,  360  and  362 , that may be supported by a rear support layer  308 . Electrodes  360  are shaded and electrodes  362  are highlighted by crosshatched lines in  FIGS. 3A-C . Further, a transparent region  364  may be located between electrodes  360  and  362  that allows light rays to pass through. In an exemplary embodiment, region  364  may be glass, plastic or other substantially transparent material. In other embodiments, region  364  may instead be devoid of any material. Region  364  may also be made of a highly reflective filler material. Display  300  may further comprise a light reflective layer  366 . Reflective layer  366  may be situated between the rear support layer  308  and the layer containing the plurality of electrodes  360 ,  362  and transparent region  364 . A first plurality of electrodes  360  may be controlled by a first transistor and a second plurality of electrodes  362  may be controlled by a second transistor. Each plurality of electrodes,  360  or  362 , may consist of more than two electrodes and may be interdigitated. The width of electrodes  360 ,  362  may decrease as the number of electrodes increases per each pixel while keeping the dimensions of the pixel constant. 
     Multiple electrodes within each pixel may provide an additional advantageous feature of the display design in  FIG. 3A . Multiple electrodes may lead to decreased lateral electric fields within the cavity containing medium  314  and mobile particles  361 ,  318 . Reducing the lateral electric fields may reduce lateral movement and migration of the particles. This may lead to more uniform display performance. The cavity formed between reflective front electrode  306  and rear electrodes  360 ,  362  and transparent region  364  may further comprise spacer units (not shown) such as beads to control the size of the gap between the front and rear electrodes. 
     The space or region between rear electrodes  360  and  362  and the reflective layer  366  provides an additional advantageous feature of the display design illustrated in  FIG. 3A . Conventional TIR image displays with front sheets comprising convex protrusions such as hemispherical protrusions, suffer from “dark pupil” problem. The reflectance of the display may be reduced as incident light rays may pass through the dark pupil region at the center of each protrusion instead of being totally internally reflected. In the invention described herein, light rays that may pass through the dark pupil regions may be reflected by reflective layer  166 . Reflected light rays may then be reflected back towards viewer  328  which may enhance the reflectance of display  300 . Regions  364  between the rear electrodes  360  and  362  may further be aligned or registered with the convex protrusions. For example, region  364  may align with a single hemispherical protrusion or row of hemispherical protrusions. 
     The exemplary embodiment of display  300  may further include an optional dielectric layer  320  located on the surface of transparent front electrode  306  and disposed between transparent front electrode  306  and medium  314 .  FIG. 3A  illustrates a dielectric layer  322  on the surface of the rear electrodes  360 ,  362 . Dielectric layer  322  may also be located on transparent region  364  in display  300  such that the dielectric layer is disposed between the rear electrodes  360 ,  362  and transparent region  364  and medium  314 . Having a dielectric layer on the rear electrodes may be optional and may depend on the composition of the rear electrodes. The dielectric layers may each be a uniform layer of at least about 20 nanometers in thickness. Dielectric compounds may be organic or inorganic in type. The most common inorganic dielectric material is silicon dioxide commonly used in integrated chips. Organic dielectric materials are typically polymers such as polyimides, fluoropolymers, polynorbornenes and hydrocarbon-based polymers lacking polar groups. In an exemplary embodiment, the dielectric layers comprises parylene. In another embodiment the dielectric layers comprise a halogenated parylene. Other inorganic or organic dielectric materials or combinations thereof may also be used. 
     The dielectric layers may each have a thickness of at least 80 nanometers. In an exemplary embodiment, the thickness is about 80-200 nanometers. Advantageously, parylene has a low dielectric constant and may be made as thin as 20 nanometers without having pinhole leakage paths. Such features may contribute to display structures having a comparatively high capacitance per unit area. The high capacitance means that the required number per unit area of charged mobile particles may be attracted to the parylene at a lower voltage than if the thickness was higher or if the dielectric constant was lower. 
     Referring again to  FIG. 3A , the display  300  shows a pixel of the display in a first optical state. The optical state may be created by absorption of light rays by the particles  318  with a negative charge polarity and with a first optical characteristic. In this state, the electrophoretically mobile particles  316  with a positive charge polarity may be moved under the influence of an applied voltage bias near dielectric layer  322  adjacent to the plurality of rear electrodes  360 ,  362 . Ideally, the plurality of electrodes  360  and  362  may be interdigitated but is not required for operation of display  300 . In this example in  FIG. 3A , the rear electrodes  360 ,  362  may have an applied voltage bias V 1  and V 2 , respectively, of −5V (It should be noted that other voltage biases of varying magnitudes may be applied as −5V is used for illustrative purposes only). The negatively charged particles  318  may be moved near the front dielectric layer adjacent the grounded front electrode surface  306  that has a +5V bias (V G ). Front electrode  306  is located on the inward surface of transparent front sheet  302  on the surface of the plurality of protrusions  304 . In this location particles  318  may enter the evanescent wave region, absorb incident light rays and frustrate TIR. This is illustrated by incident light rays  368  and  370  in  FIG. 3A  that may be absorbed by negatively charged particles  318  whereby the portion of the display in  FIG. 3A  observed by viewer  328  may exhibit the optical characteristic (i.e. color) of the negatively charged particles  318 . 
       FIG. 3B  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a second optical state according to one embodiment of the disclosure. Display  300  in  FIG. 3B  is the same as that described in  FIG. 3A  in the preceding paragraphs but illustrates how a second optical state may be formed. Display  300  in  FIG. 3B  shows a pixel of the display in a second optical state created by absorption of incident light rays by particles  316  with a positive charge polarity and with a second optical characteristic. In this state, the electrophoretically mobile particles  318  of a negative charge polarity may be moved under the influence of an applied voltage bias near optional dielectric layer  322  adjacent to the plurality of rear electrode surfaces  360  and  363 . In the example in  FIG. 3B , rear electrodes  360 ,  362  may have an applied voltage bias V 1  and  2 , respectively, of +5V (It should be noted that other voltage biases of varying magnitudes may be applied as +5V is used for illustrative purposes only). The particles  116  with a positive charge polarity may be moved near the front dielectric layer adjacent the grounded front electrode surface  106  that has a −5V bias (V G ) into the evanescent wave region such that TIR is frustrated and incident light rays may be absorbed. This is illustrated by incident light rays  372  and  374  that may be absorbed by the positively charged particles  316 . Thus the portion of the display in  FIG. 3B  observed by viewer  328  exhibits the optical characteristic (i.e. color) of the positively charged particles  316 . 
       FIG. 3C  schematically illustrates a cross-section of a portion of a total internal reflection image display comprising oppositely charged particles, interdigitated rear electrodes and a reflective layer in a third optical state according to one embodiment of the disclosure. Display  300  in  FIG. 3C  is the same as that described in  FIGS. 3A-B  in the preceding paragraphs but exhibits a third optical state. In this state, the mobile particles  316  with a positive charge polarity may be moved under the influence of an applied voltage bias, V 2 , of −5V near rear electrode  362 . The mobile particles  318  with a negative charge polarity may be moved under the influence of an applied voltage bias, V 1 , of +5 V near dielectric layer  322  adjacent to rear electrode  360  (rear electrodes are shaded in  FIG. 3C ). In this state of the display in  FIG. 3C  there may be no particles in the evanescent wave region near the front dielectric layer  320  adjacent the grounded front electrode  306  which has a voltage bias, V G , of 0V. Incident light rays  376  and  378  may instead be totally internally reflected back towards viewer  328  as reflected light rays  380  and  382 , respectively, to create a light or bright state. This is a third optical state of display  300 . In this third optical state, regions  364  and reflective layer  366  may further enhance the reflectance as there are no particles in the evanescent wave region to absorb incident light rays. In this state, light rays that are not totally internally reflected may pass through the center of the protrusions of front sheet  302  and may be reflected by layer  366  back towards viewer  328 . 
     In displays  100 ,  200  and  300  illustrated in  FIGS. 1A-C ,  2 A-C and  3 A-C and described in the preceding paragraphs, three optical states of each the displays have been described. It should be noted that a continuum of intermediate grey states may also be capable of being displayed by the reflective image displays described herein. For example, by varying the magnitude of the applied voltage bias and the time period the voltage bias is applied only partial frustration of TIR may be carried out by a portion of the particles. 
     In some embodiments, a porous reflective layer may be used in combination with the reflective image displays comprising more than two electrodes described herein. The porous reflective layer may be interposed between the front and rear electrode layers. In other embodiments, the rear electrode may be located on the surface of the porous electrode layer. The porous reflective layer may be formed of a track etched polymeric material such as polycarbonate, polyester, polyimide or some other polymeric material or glass with a thickness of at least about 10 microns. The porous nature of the film would allow for the electrophoretically mobile panicles to pass through the pores. The average diameter of the pores in the porous reflective layer may be substantially greater (e.g., about 10 times greater) than the average diameter of the mobile particles. The pores in the porous reflective layer may constitute large fraction (e.g., at least 10%) of the total surface area of the porous reflective layer to permit substantially unimpeded passage of the mobile particles through the pores. 
     Various control mechanisms for the invention may be implemented fully or partially in software and/or firmware. This software and/or firmware may take the form of instructions contained in or on a non-transitory computer-readable storage medium. Those instructions may then be read and executed by one or more processors to enable performance of the operations described herein. The instructions may be in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. Such a computer-readable medium may include any tangible non-transitory medium for storing information in a form readable by one or more computers, such as but not limited to read only memory (ROM); random access Memory (RAM); magnetic disk storage media; optical storage media; a flash memory, etc. 
     In some embodiments, a tangible machine-readable non-transitory storage medium that contains instructions may be used in combination with the reflective displays comprising more than two electrodes described herein. In other embodiments the tangible machine-readable non-transitory storage medium may be further used in combination with one or more processors. 
       FIG. 4  shows an exemplary system for controlling a display according to one embodiment of the disclosure. In  FIG. 4 , display  400  is controlled by controller  440  having processor  430  and memory  420 . Other control mechanisms and/or devices may be included in controller  440  without departing from the disclosed principles. Controller  440  may define hardware, software or a combination of hardware and software. For example, controller  440  may define a processor programmed with instructions (e.g., firmware). Processor  430  may be an actual processor or a virtual processor. Similarly, memory  420  may be an actual memory (i.e., hardware) or virtual memory (i.e., software). 
     Memory  420  may store instructions to be executed by processor  430  for driving display  400 . The instructions may be configured to operate display  400 . In one embodiment, the instructions may include biasing electrodes associated with display  400  (not shown) through power supply  450 . When biased, the electrodes may cause movement of electrophoretic particles towards or away from a region proximal to the surface of the plurality of protrusions at the inward surface of the front transparent sheet to thereby absorb or reflect light received at the inward surface of the front transparent sheet. By appropriately biasing the electrodes, mobile light absorbing particles (e.g., particles  116  and  118  in  FIGS. 1A-C , particles  216  and  218  in  FIGS. 2A-C , particles  316  and  318  in  FIGS. 3A-C ) may be moved near the surface of the plurality of protrusions at the inward surface of the front transparent sheet into the evanescent wave region in order to substantially or selectively absorb the incoming light. Absorbing the incoming light creates a dark or colored state. By appropriately biasing the electrodes, mobile light absorbing particles (e.g., particles  116  and  118  in  FIGS. 1A-C , particles  216  and  218  in  FIGS. 2A-C , particles  316  and  318  in  FIGS. 3A-C ) may be moved away from the surface of the plurality of protrusions at the inward surface of the front transparent sheet and out of the evanescent wave region in order to reflect the incoming light. Rejecting the incoming light creates a light state. 
     In other embodiments, the reflective image displays comprising more than two electrodes described herein may further include at least one sidewall (may also be referred to as cross-walls). Sidewalls limit particle settling, drift and diffusion to improve display performance and bistability. Sidewalls may be located within the light modulation layer. Sidewalls may completely or partially extend from the front electrode, rear electrode or both the front and rear electrodes. Sidewalls may comprise plastic or glass. Sidewalls may create wells or compartments (not shown) to comprise the electrophoretically mobile particles. The sidewalls or cross-walls may be configured to create wells or compartments in, for example, square-like, triangular, pentagonal or hexagonal shapes or a combination thereof. The walls may comprise a polymeric material and patterned by conventional techniques including photolithography, embossing or molding. The walls help to confine the mobile particles to prevent settling and migration of said particles that may lead to poor display performance over time. In certain embodiments the displays may comprise cross-walls that completely bridge the gap created by the front and rear electrodes in the region where the liquid medium and the mobile particles resides. In certain embodiments, the reflective image display described herein may comprise partial cross-walls that only partially bridge the gap created by the front and rear electrodes in the region where the liquid medium and the mobile particles reside. In certain embodiments, the reflective image displays described herein may further comprise a combination of cross-walls and partial cross-walls that may completely and partially bridge the gap created by the front and rear electrodes in the region where the liquid medium and the mobile particles reside. 
     The reflective image displays comprising more than two electrodes described herein may further comprise a color filter array layer. The color array layer may comprise at least one or more of red, green and blue or cyan, magenta and yellow filters. 
     The reflective image displays comprising more than two electrodes described herein may further comprise a directional front light system. The directional front light system may include a light source, light guide and an array of light extractor elements on the top surface of the top sheet in each display. The directional light system may be positioned between the outward surface of the outward sheet and the viewer. The front light source may define a light emitting diode (LED), cold cathode fluorescent lamp (CCFL) or a surface mount technology (SMT) incandescent lamp. The light guide may be configured to direct light to the front entire surface of the transparent outer sheet while the light extractor elements direct the light in a perpendicular direction within a narrow angle, for example, centered about a 30° cone, towards the front sheet. A directional front light system may be used in combination with cross-walls or a color filter layer in the display architectures described herein or a combination thereof. 
     In other embodiments, any of the reflective image displays comprising more than two electrodes described herein may further include at least one edge seal. An edge seal may be a thermally or photo-chemically cured material. The edge seal may comprise one or more of an epoxy, silicone or other polymer based material. 
     In other embodiments, any of the reflective image displays comprising more than two electrodes described herein may further include a light diffusive layer to “soften” the reflected light observed by the viewer. In other embodiments a light diffusive layer may be used in combination with a front light. 
     In the display embodiments described herein, they may be used in such applications such as in, but not limited to, electronic book readers, portable computers, tablet computers, cellular telephones, smart cards, signs, watches, wearables, shelf labels, flash drives and outdoor billboards or outdoor signs comprising a display. 
     The following exemplary and non-limiting embodiments provide various implementations of the disclosure. Example 1 is directed to a method, wherein a method to display an image, comprising: receiving one or more incoming light rays at a first surface of a transparent front sheet, the front sheet having a refractive index; forming a first optical state by directing a plurality of first electrophoretically mobile particles to a region adjacent the first electrode and directing a plurality of second electrophoretically mobile particles to a region adjacent a second and a third electrodes; forming a second optical state by directing the plurality of second electrophoretically mobile particles to the region adjacent the first electrode and directing the plurality of first electrophoretically mobile particles to the region adjacent the second and the third electrodes; and forming a third optical state by directing the plurality of first electrophoretically mobile particles to a region adjacent the second electrode and directing the second plurality of electrophoretically mobile particles to a region adjacent the third electrode. 
     Example 2 is directed to the method of example 1, wherein the first optical state further comprises substantially or selectively absorbing the one or more incoming light rays by the plurality of first electrophoretically mobile particles thereby exhibiting the optical characteristic of the first electrophoretically mobile particles. 
     Example 3 is directed to the method of examples 1 or 2, wherein the second optical state further comprises substantially or selectively absorbing the one or more incoming light rays by the plurality of second electrophoretically mobile particles thereby exhibiting the optical characteristic of the second electrophoretically mobile particles. 
     Example 4 is directed to the method of any preceding example, further comprising receiving the one or more light rays at the first surface of the transparent front sheet and exiting the one or more light rays at a second surface of the transparent front sheet, the second surface having a plurality of hemispherical or convex protrusions. 
     Example 5 is directed to the method of any preceding example, further comprising receiving the one or more light rays at the first surface of the transparent front sheet and exiting the one or more light rays at a second surface of the transparent front sheet, the second surface having a plurality of hemispherical or convex protrusions. 
     Example 6 is directed to the method of any preceding example, further comprising biasing the first electrode at a first voltage and biasing each of the second and third electrodes at a second voltage. 
     Example 7 is directed to the method of any preceding example, further comprising biasing the first electrode at a first voltage, biasing the second electrode at a second voltage and biasing the third electrode at a third voltage. 
     Example 8 is directed to the method of any preceding example, further comprising providing the second and the third biases substantially opposite in polarity. 
     Example 9 is directed a multi-electrode display device, comprising: a transparent front sheet to receive one or more incoming light rays at a first surface thereof, the front sheet having a refractive index; a first electrode positioned proximal to the front sheet; a rear support facing the first electrode and forming a cavity therebetween; a second electrode positioned adjacent to the cavity; a third electrode positioned adjacent to second electrode and the cavity; and a controller to communicate with each of the first, second and the third electrodes, the controller configured to independently activate one or more of the first, second or third electrodes to cause total internal reflection of the one or more incoming light rays through the front sheet to thereby substantially exclude the incoming light rays from the cavity or to cause frustration of total internal reflection. 
     Example 10 is directed to the display of example 9, wherein the second and third electrodes are positioned adjacent each other. 
     Example 11 is directed to the display of examples 9 or 10, wherein the second and third electrodes are positioned as an array of interdigitated electrodes. 
     Example 12 is directed to the display of any preceding examples, wherein at least one of the plurality of protrusions defines a hemispherical or a convex protrusion. 
     Example 13 is directed to the display of any preceding example, further comprising at least one of a first plurality of electrophoretically mobile particles and a second plurality of electrophoretically mobile particles, the first electrophoretically mobile particles having a first charge and the second electrophoretically mobile particles having a second charge. 
     Example 14 is directed to the display of any preceding example, wherein the first charge and the second charge are opposite in polarity. 
     Example 15 is directed to the display of any preceding example, wherein the controller is further configured to bias each of the first, second and third electrodes independently to modulate total internal reflection (TIR) by moving the first electrophoretically mobile particles adjacent to the first electrode and moving the second electrophoretically mobile particles adjacent to the second and third electrodes. 
     Example 16 is directed to the display of any preceding example, wherein the controller is further configured to bias each of the first, second and third electrodes independently to provide total internal reflection (TIR) by moving the first electrophoretically mobile particles adjacent the second electrode and moving the second electrophoretically mobile particles adjacent the third electrode. 
     Example 17 is directed to the display of any preceding example, wherein the front sheet further comprises a plurality of protrusions on a second surface thereof. 
     Example 18 is directed to the display of any preceding example, further comprising a dielectric layer formed over at least one of the first, second or third electrodes. 
     Example 19 is directed to the display of any preceding example, comprising: a transparent front sheet to receive one or more incoming light rays at a first surface and exiting the one or more light rays at a second surface thereof; a pixel having: a first electrode positioned at or near the second surface of the front sheet; a second electrode and a third electrode arranged to form a cavity with the first electrode, the first and the second electrodes arranged; and a controller to communicate with each of the first, second and the third electrodes, the controller configured to independently activate one or more of the first, second or third electrodes to cause a total internal reflection of the one or more incoming light rays through the front sheet to thereby substantially exclude the incoming light rays from the cavity or to cause frustration of total internal reflection. 
     Example 20 is directed to the display of any preceding example, further comprising a fluidic medium disposed in the cavity. 
     Example 21 is directed to the display of any preceding example, further comprising at least one of a first electrophoretically mobile particles and a second electrophoretically mobile particles disposed in the medium, the first electrophoretically mobile particles having a first charge polarity and the second electrophoretically mobile particles having a second charge polarity. 
     Example 22 is directed to the display of any preceding example, wherein the controller is configured to engage one or more of the first, second or third electrodes to draw the first electrophoretically mobile particles to the first electrode to cause frustration of total internal reflection of the one or more incoming light rays through the front sheet and to move the second electrophoretically mobile particles adjacent to the second and third electrodes. 
     Example 23 is directed to the display of any preceding example, wherein the second electrode and the third electrode are arranged to form an array. 
     Example 24 is directed to the display of any preceding example, further comprising a plurality of second and third electrodes arranged in a checkered pattern to form a pixel with the first electrode. 
     Example 25 is directed to the display of any preceding example, further comprising a dielectric layer to cover one of the first, second or third electrodes. 
     Example 26 is directed to the display of any preceding example, wherein the controller is configured to engage the second electrode and third electrode with substantially opposite biases. 
     Example 27 is directed to the display of any preceding example, wherein the controller is configured to engage the first electrode and second electrode with substantially opposite biases. 
     While the principles of the disclosure have been illustrated in relation to the exemplary embodiments shown herein, the principles of the disclosure are not limited thereto and include any modification, variation or permutation thereof.