Abstract:
A transparent image producing display or receiver which uses a suspension fluid for producing pixels of an image includes at least one image-forming layer having a structure which defines a plurality of pixels, with the structure receiving a suspension fluid having field-driven particles, which move in response to an externally applied field, where, in a first condition, the field-driven particles produce a first level of transmitted incident light and, in an second condition, produce a second level of transmitted incident light.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. patent application Ser. No. 09/012,842 filed Jan. 23, 1998, entitled “Addressing Non-Emissive Color Display Device” to Wen et al; U.S. patent application Ser. No. 09/035,516 filed Mar. 5, 1998, entitled “Heat Assisted Image Formation in Receivers Having Field-Driven Particles” to Wen et al; U.S. patent application Ser. No. 09/034,066 filed Mar. 3, 1998, entitled “Printing Continuous Tone Images on Receivers Having Field-Driven Particles” to Wen et al; U.S. patent application Ser. No. 09/037,229 filed Mar. 10, 1998, entitled “Calibrating Pixels in a Non-emissive Display Device” to MacLean et al; U.S. patent application Ser. No. 09/054,092 filed Apr. 2, 1998, entitled “Color Image Formation In Receivers Having Field-Driven Particles” to Wen et al; U.S. patent application Ser. No. 09/075,081 filed May 8, 1998, entitled “Color Image Device With Integral Heaters” to MacLean et al. The disclosure of these related application is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to an image-forming device having field-driven particles. 
     BACKGROUND OF THE INVENTION 
     There are several types of field-driven particles in the field of non-emissive displays. One class uses the so-called electrophoretic particle that is based on the principle of movement of charged colloidal particles in an electric field. In an electrophoretic image-forming device, the charged particles containing different reflective optical densities can be moved by an electric field to or away from the viewing side of the device, which produces a contrast in the optical density. Another class of field-driven particles are particles carrying an electric dipole. Each pole of the particle is associated with a different optical densities (bi-chromatic). The electric dipole can be aligned by a pair of electrodes in two directions, which orient each of the two polar surfaces to the viewing direction. The different optical densities on the two halves of the particles thus produces a contrast in the optical densities. 
     Electrophoretic image-forming devices are limited to reflective applications. It is desired to produce a transparent electrophoretic image-forming device for transmissive applications. 
     Electrophoretic image-forming devices are also limited in their ability to produce high contrast and sufficient color gamut. It is desired to produce an electrophoretic image-forming device with improved contrast and color gamut. 
     To produce a high quality image, it is essential to form a plurality of image pixels by varying the electric field on a pixel wise basis. The electric fields can be produced by a plurality pairs of electrodes embodied in the display as disclosed in U.S. Pat. No. 3,612,758. One difficulty is in displaying color images. The field-driven particles of different colors need to be provided in discrete color pixels. This approach requires the colored particles to be placed in precise registration corresponding to the electrodes. This approach is therefore complex and expensive. 
     An additional problem in the displays comprising field-driven particles is forming images that are stable. Typically the images on these displays must be periodically refreshed to keep the image from degrading. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved way of providing field-driven electrophoretic suspensions which can readily form images in displays and receivers. 
     It is a further object of the present invention to provide an electrophoretic image with improved contrast and color gamut. 
     These objects are achieved by a display which uses a suspension fluid for producing pixels of an image, comprising: 
     a) at least one image-forming layer having a structure which defines a plurality of pixels, the structure including means for receiving a suspension fluid having light absorbing field-driven particles where, in a first condition, the field-driven particles present a reduced surface area to absorb a reduced portion of incident light and, in a second condition, present a wider surface area to absorb an increased portion of incident light; 
     b) at least one electric field forming means for selectively applying electric fields to the image-forming layer which acts upon at least one pixel and its field-driven particles in the suspension fluid; and 
     c) electronic control means coupled to the electric field forming means so that electric fields are selectively applied at locations on the image-forming layer corresponding to pixels in response to a stored image thereby effecting changes in the position of the field-driven particles to cause the production of an image in the image-forming layer corresponding to a stored image. 
     These objects are also achieved by a transparent image producing receiver which uses a suspension fluid for producing pixels of an image, comprising: at least one image-forming layer having a structure which defines a plurality of pixels, with the structure including means for receiving a suspension fluid having field-driven particles, which move in response to an externally applied field, where, in a first condition, the field-driven particles produce a first level of transmitted incident light and, in an second condition, produce a second level of transmitted incident light. 
     Advantages 
     An advantage of the present invention is that a transparent electrophoretic image-forming display and receiver are provided for use in transmissive applications. 
     A further advantage is that a multiple layer color electrophoretic imaging displays and receivers are provided resulting in improved contrast and color gamut. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an electronic display apparatus in accordance to the present invention; 
     FIG. 2 shows a cross section of the display of FIG. 1; 
     FIG. 3 shows a cross section of the cyan image-forming layer taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a graphical illustration of the melting temperatures of the material in microcapsules and the temperature ranges for writing different color images; 
     FIG. 5 schematically shows a flow diagram for producing color images on a display having color field-driven particles in accordance with the present invention; 
     FIG. 6 shows a cross section of an alternate embodiment of the display of FIG. 1; 
     FIG. 7 shows a cross section of a image receiver in accordance to the present invention; and 
     FIG. 8 shows a cross section of an alternate embodiment of the receiver of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the electronic display apparatus  10  in accordance to the present invention. The electronic display apparatus  10  includes a processing unit  20 , a drive electronics  30  which applies electric fields, a heater control unit  40 , and a display  50  comprised of field-driven particles (see FIGS.  2  &amp;  3 ). The display  50  includes a temperature sensor  60 . A digital image is presented to the processing unit  20 . The processing unit  20  controls the drive electronics  30  and the heater control unit  40 . The temperature sensor  60  detects the temperature of the display and sends electrical signals corresponding to the temperature to the heater control unit  40 . The heater control unit  40  regulates the temperature of the display  50 . The drive electronics  30  provide the electrical signals required to write the image. Thus, the processing unit controls  20  forms the digital image on the display  50 . The image-forming process will be discussed in detail below. 
     FIG. 2 shows a cross sectional view of a portion of the display  50  of FIG.  1 . The cross section shows a small portion of the display element. The display  50  is comprised of a substrate  240 , a heater  270  disposed on the substrate  240 , a passivation layer  260  is disposed above the heater  270 , an array of bottom electrodes  280  disposed above the passivation layer  260 , a reflective layer  300  disposed above the array of bottom electrodes  280 , a yellow image-forming layer  120  disposed above the reflective layer  300 , a magenta image-forming layer  110  disposed above the yellow image-forming layer  120 , a cyan image-forming layer  100  disposed above the magenta image-forming layer  110 , a top electrode  290  disposed above the magenta image-forming layer, a polymer film  230  disposed above the top electrode  290 , and a protective top coat  250  disposed over the polymer film  230 . The heater  270  is connected to the heater control unit  40  (not shown). The top electrode  290  is formed of transparent conducting materials such as indium tin oxide for the viewing of the image formed in the image-forming layers. The temperature sensor  60  of FIG. 1 is attached to the substrate to monitor the temperature of the display  50 . The temperature sensor  60  is connected to the heater control unit  40  of FIG.  1 . 
     Alternate electrode configurations can be used without substantially modifying the invention. One such configuration would provide a pair of transparent arrays of electrodes for each image forming layer: the yellow image-forming layer  120 , the magenta image-forming layer  110 , and the cyan image-forming layer  100 . Each array would be individually driven by the drive electronics  30 . 
     The substrate  240  controls the flexibility and durability of the display  50 . The substrate  240  can be a polymer layer. In some applications, rigid substrate such as glass and ceramics can also be used. The heater  270  will be discussed below. The passivation layer  260  is provided to electrically isolate the bottom electrodes  280  from the heater  270 . The arrays of bottom electrodes  280  is an active matrix arranged in a grid pattern. Each electrode corresponds to a pixel. The array of bottom electrodes  280  and the top electrode  290  are connected to the drive electronics  30  of FIG. 1 (not shown) to apply electric fields to the image forming layers  100 ,  110  &amp;  120 . An electric voltage is applied by drive electronics  30  to the pair of electrodes at each pixel location to produce the desired optical density at that pixel. A protective top coat  250  is disposed above the top electrode  290  to protect the display  50  and to provide a surface treatment (matte or gloss). Details of the addressing circuitry for the electrodes are disclosed in commonly assigned U.S. patent application Ser. No. 09/034,066 filed Mar. 3, 1998, entitled “Printing Continuous Tone Images on Receivers Having Field-Driven Particles” to Wen et al, the disclosure of which is incorporated herein. 
     The heater  270  is connected to the heater control unit  40  of FIG.  1 . The heater  270  consists of an array of heater elements. Each heater element corresponds to a row in the display  50 . The heater  270  can alternately be segmented without substantially changing the present invention. For example, an array of heaters could be formed to correspond to individual pixels, single columns, multiple columns, single rows, multiple rows, individual pixels, and other regions. The heater  270  is embodied by an array of carbon film resistors. The heaters may also be formed of a diode junction or any material which resistively consumes electrical power (creating heat). Each member of the heater  270  is electrically isolated. Since the heater  270  is adjacent to the image-forming layer(s), only a portion of the display needs to be heated to cause a change in temperature in the thermomeltable materials  210  (discussed below). Additionally, the heater is in direct contact with the display providing improved thermal conductivity. These two factors each allow the energy requirements for the display to be substantially reduced. 
     Three image-forming layers are shown, a cyan image-forming layer  100 , a magenta image-forming layer  110 , and a yellow image-forming layer  120 . Each layer is similar. The cyan image-forming layer  100  is formed of cyan light absorbing particles  200  and thermomeltable material  210  with a transition temperature of Tcyan. The magenta image-forming layer  110  is formed of magenta light absorbing particles  200  and thermomeltable material  210  with a transition temperature of Tmagenta. The yellow image-forming layer  120  is formed of yellow light absorbing particles  200  and thermomeltable material  210  with a transition temperature of Tyellow. The particles  200  are each is designed to absorb a specific color of light while allowing other colors to pass with minimal absorption or scattering. 
     The reflective layer  300  is a polymeric film incorporating highly scattering particles, in this case toil particles. The image-forming layers  100 ,  110 , and  120  work in conjunction with the reflective layer  300  to produce an image. Each image-forming layer is transparent. Light incident on the display panel  50  is selectively absorbed by each image-forming layer. The reflective layer  300  diffusely reflects the light through the image-forming layers for further selective absorption. The resultant image is viewed through the protective top coat  250 . 
     FIG. 3 shows a cross section of the cyan image-forming layer  100  taken along line  3 — 3  of FIG.  2 . The cyan image-forming layer  100  is representative of the form of the magenta and yellow image-forming layers  110 ,  120 . The cyan image-forming layer  100  includes a polymer film  230 . A pixel defining structure includes a constricting screen  220  that is formed above the polymer film  230 . The constricting screen  220  is filled with particles  200  suspended in a thermomeltable material  210 . An additional polymer film  230  is deposited above the constricting screen  220 . The polymer film  230  is transparent and serves to contain and seal the material into the constricting screen  220 . The polymer film  230  may be shared by adjacent image-forming layers. The constricting screen  220  is a polymeric material. The constricting screen  220  is a layer with cavities  225  incorporated therein. The cavities  225  are constricting in nature. The cavities  225  can be described as funnel shaped, with a wider portion  225 A on one end and a restricted portion  225 B on the other end. The cavities  225  are arranged in a close packed manner to maximize the coverage of the cavities  225 . The wider portion  225 A of the cavities  225  are preferably chosen to be either rectangular or hexagonal in shape, although any shape may be chosen without substantially modifying the present invention. The constricting screen  220  can conveniently be formed by a molding process. The constricting screen  220  may be formed by a variety of known manufacturing means without changing the nature of the invention. 
     The particles  200  are electrophoretic particles which move in the presence of an electric field which can be applied by drive electronics such as the drive electronics  30  shown in FIG.  1 . When a positive voltage the particles  200  move toward the wider portion  225 A presenting a wider surface area to absorb an increased portion of the incident light; when a negative voltage is applied the particles  200  move towards the restricted portion  225 B of the cavity  225  presenting a reduced surface area to absorb a reduced potion of the incident light. The particles  200  are cyan absorbing red light. In the magenta image-forming layer  110  of FIG. 2, the particle  200  are magenta absorbing green light. In the yellow image-forming layer  120  of FIG. 2 the particles  200  are yellow absorbing blue light. The thermomeltable material  210  serves as a image-forming layer selection mechanism and an electrophoretic suspension fluid. When the thermomeltable material  210  is above its transition temperature the particles  200  move in response to an electric field. When the thermomeltable material  210  is below its transition temperature the particles  210  are stabilized, fixing the formed image. 
     The constricting screen  220  is the functional element which together with the movement of the particles  200  forms the image. When the particles  200  are in the wider portion  225 A of a cavity in constricting screen  220 , the particles  200  absorb the light of their respective color, in this case cyan, incident on the cavity  225 . When the particles  200  are in the restricted portion  225 B of the cavity  225 , the particles absorb only that portion of light incident on the restricted portion  225 B of the cavity  225 , the vast majority of light is passed. In this case the color response is a function of the surface coverage of the particles in the cavity  225 . When the particles are in the wider portion  225 A of the cavity  225  the surface coverage is high. When the particles are in the restricted portion  225 B the surface coverage is low. When the particles are in the restricted portion the particles obscure each other reducing the average absorption of light. 
     The image-forming layers are transparent. The layers are be stacked and the images are be combined. This is especially important in forming a high quality color display. Each layer independently controls one single color channel, and a composite high quality full color image is be formed. 
     The term thermomeltable material will be understood to mean a material which substantially decreases its viscosity when its&#39; temperature is raised from below to above a transition temperature (range). The transition temperature range typically corresponds to a transition in chemical phase or physical configuration. Examples of the transition include melting (and freezing), solidifying, hardening, glass transition, chemical or physical polymerization, cross-linking or gelation, aggregation or association of particles or molecules. When the temperature of the thermomeltable material is varied from above to below the transition temperature, the viscosity typically increases at least a factor of five, and preferably ten times or larger. The mobility of the field-driven particles is inversely related to the viscosity of the thermomeltable material where in the field-driven particles are immersed. The materials for the thermomeltable materials are each different having different transition temperature ranges and are discussed below. 
     A substantial change in the viscosity of the thermomeltable material is defined by the effects on the field-driven particles. When immersed in such thermomeltable materials, the field-driven particles are immobile at temperatures below the transition temperature: that is, the field-driven particles do not change their physical configurations in the presence of an external (e.g. electric) field or thermodynamic agitation. At temperature above the transition temperature, the field-driven particles can respond (rotation or translation) to the external field to permit the change in color reflective densities. Typically, a thermomeltable material needs to changes viscosity a factor of five or larger through the transition. 
     As noted above the thermomeltable materials each have different transition temperature ranges. The thermomeltable materials are chosen to have transition temperature ranges which are different and do not overlap. The transition temperature range is preferably chosen to be well above room temperature to stabilize the image at room temperature. Examples of the thermomeltable materials and their transition temperatures are listed in Table I. The thermomeltable material  210  for cyan field-driven particles  200  is selected to be carnuba wax (corypha cerifera) which has a transition temperature range of 86-90° C. The thermomeltable material  210  for magenta field-driven particles  200  is selected to be beeswax (apis mellifera) which has a transition temperature range of 62-66° C. The thermomeltable material  210  for yellow field-driven particles  200  is 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Transition 
                   
               
               
                   
                 temperature 
               
               
                 Thermomeltable Material 
                 range (° C.) 
                 Comment 
               
               
                   
               
             
             
               
                               Myrtle Wax 
                 39-43       1   
                 Myria Cerifera 
               
               
                 Beeswax 
                 62-66 1   
                 Apis Melifera 
               
               
                 Carnuba Wax 
                 86-90 1   
                 Corypha Cerifera 
               
               
                 Eicosane C 20 H 42   
                 38 1   
               
               
                 Triacontane C 30 H 62   
                 66.1 1   
               
               
                 Pentatriacontane C 35 H 72   
                 74.7 1   
               
               
                 Tetracosane C 24 H 50   
                 51.1 1   
               
               
                 X-8040 Baker-Petrolite 
                 79 2   
                 Alpha olefin/maleic anhydride 
               
               
                   
                   
                 copolymer 
               
               
                 Vybar 260 Baker-Petrolite 
                 54 2   
                 Ethylene derived hydrocarbon 
               
               
                   
                   
                 polymer 
               
               
                 Vybar 103 Baker-Petrolite 
                 74 2   
                 Ethylene derived hydrocarbon 
               
               
                   
                   
                 polymer 
               
               
                   
               
               
                   1                Handbook of Chemistry and Physics, CRC Publishers, 42 nd  Edition, 1960-1961  
               
               
                   2 Technical Information, Baker-Petrolite, Tulsa, OK. 1998  
               
             
          
         
       
     
     selected to be myrtle wax (myria cerifera) which has a transition temperature range of 39-43° C. The thermomeltable materials are each waxes which solidify as the thermomeltable material temperature is decreased through the transition temperature range. Below the transition temperature range, the viscosity of the thermomeltable materials is substantially higher (solid) than at temperatures above the transition temperature range. Although waxes are used in the present invention other materials are equally compatible, provided they are selected to have differing transition temperature ranges. Several thermomeltable materials are shown in Table 1. It is understood that other thermomeltable materials may used in the present invention without substantially affecting the performance. 
     FIG. 4 shows a plot of the exemplified transition temperature ranges of the thermomeltable materials  210  of display  50  (FIG.  3 ). In this example the thermomeltable material  210  for cyan field-driven particles  200  have a transition temperature range Tcyan. The cyan plane is written at temperatures above this transition temperature range. The thermomeltable material  210  for magenta field-driven particles  200  have a transition temperature range Tmagenta. The magenta plane is written at temperatures above this transition temperature range and below the Tcyan transition temperature range. The thermomeltable material  210  for yellow field-driven particles  200  have a transition temperature range Tyellow. The yellow plane is written at temperatures above this transition temperature range and below the Tmagenta transition temperature range. The order of the transition temperature ranges can be changed with appropriate changes to the operating procedure. 
     Referring to FIG. 5, a typical operation of the electronic display apparatus  10  of FIG. 1 is described in the following. A digital image is presented to the processing unit  20  (FIG.  1 ). Processing unit  20  receives the digital image storing it in internal storage. All processes are controlled by processing unit  20  via drive electronics  30  (FIG. 1) and heater control unit  40  (FIG.  1 ). The processing unit  20 , the drive electronics  30 , and the heater control unit  40  will be collectively referred to as control electronics. 
     In a first operation heat display  401 , the display  50  (FIG. 1) is heated by the heater  270  (FIG. 2) to a temperature above the transition temperature range for the thermomeltable material  210  for cyan field-driven particles  200  (FIG.  2 ). The amount of the heating power is controlled by heater control unit  40  (FIG.  1 ), using information from the temperature sensor  60  (FIG.  1 ). At this temperature the thermomeltable material  210  for cyan field-driven particles  200  is in a low viscosity state. 
     After operation heat display  401 , operation write cyan plane  402  is performed. Each pixel of the cyan plane is produced by an electric field applied by the drive electronics  30 . Each pixel location is driven according to the input digital image to produce the desired optical density. The voltages are applied as a waveform, the first state of the waveform a positive voltage is applied the cyan field-driven particle  200  (FIG. 3) to move to the wider portion  225 A (FIG. 3) of cavity  225  (FIG.  3 ), erasing the cyan plane. In the second state of the waveform a negative voltage is applied for at a specific amplitude and duration, as determined by calibration data, causing a desired cyan optical density to be produced. For a more detailed description see commonly assigned U.S. patent application Ser. No. 09/034,066 filed Mar. 3, 1998, entitled “Printing Continuous Tone Images on Receivers Having Field-Driven Particles” to Wen et al, the disclosure of which is incorporated herein. The field-driven particles for the other colors have been written with the cyan plane. This side effect will be eliminated by the erasure of these colors after the stabilization of the cyan plane. 
     After the operation write cyan plane  402 , an operation stabilize cyan plane  403  is performed. This is accomplished by cooling the display below the transition temperature range for the thermomeltable material  210  for cyan field-driven particles  200 . At this temperature the thermomeltable material  210  for cyan field-driven particles  200  is in a high viscosity state and the mobility of the cyan field-driven particles  200  is reduced, stabilizing the cyan plane on the display  50 . 
     After the operation stabilize cyan plane  403 , the operation heat display  411  is performed. The display  50  (FIG. 1) is heated by the heater  270  (FIG. 2) to a temperature above the transition temperature range for the thermomeltable material  210  for magenta field-driven particles  200  (FIG. 3) and below the transition temperature range for the thermomeltable material  210  for cyan field-driven particles  200  (FIG.  3 ). The amount of the heating power is controlled by heater control unit  40  (FIG.  1 ), using information from the temperature sensor  60  (FIG.  1 ). At this temperature the thermomeltable material  210  for magenta field-driven particles  200  is in a low viscosity state. 
     After operation heat display  411 , operation write magenta plane  412  is performed. Each pixel of the magenta plane is produced by an electric field applied by the drive electronics  30 . Each pixel location is driven according to the input digital image to produce the desired optical density. The field-driven particles for the yellow plane has been written with the magenta plane. This side effect will be eliminated by the erasure of the yellow plane colors after the stabilization of the magenta plane. 
     After the operation write magenta plane  412 , an operation stabilize magenta plane  413  is performed. This is accomplished by cooling the display below the transition temperature range for the thermomeltable material  210  for magenta field-driven particles  200 . At this temperature the thermomeltable material  210  for magenta field-driven particles  200  is in a high viscosity state and the mobility of the magenta field-driven particles  200  is reduced, stabilizing the magenta plane on the display  50 . 
     After the operation stabilize magenta plane  413 , the operation heat display  421  is performed. The display  50  (FIG. 1) is heated by the heater  270  (FIG. 2) to a temperature above the transition temperature range for the thermomeltable material  210  for yellow field-driven particles  200  (FIG. 2) and below the transition temperature range for the thermomeltable material  210  for magenta field-driven particles  200  (FIG.  3 ). The amount of the heating power is controlled by heater control unit  40  (FIG.  1 ), using information from the temperature sensor  60  (FIG.  1 ). At this temperature the thermomeltable material  210  for yellow field-driven particles  200  is in a low viscosity state. 
     After operation heat display  421 , operation write yellow plane  422  is performed. Each pixel of the yellow plane is produced by an electric field applied by the drive electronics  30 . Each pixel location is driven according to the input digital image to produce the desired optical density. 
     After the operation write yellow plane  422 , an operation stabilize yellow plane  423  is performed. This is accomplished by cooling the display below the transition temperature range for the thermomeltable material  210  for yellow field-driven particles  200 . At this temperature the thermomeltable material  210  for yellow field-driven particles  200  is in a high viscosity state and the mobility of the yellow field-driven particles  200  is reduced, stabilizing the yellow plane on the display  50 . This complete the formation of the image. The image is now displayed. 
     Briefly reviewing the operation of the control electronics. The heater control unit  40  of FIG. 1 is coupled to the heater  270  of FIG. 2 for applying heat to control the temperature of the display  50  to selectively control the response of the field-driven particles  200  when an electric field is applied and coupled to the array of bottom electrodes  280  for selectively applying voltages to the array of bottom electrodes  280  so that electric fields are applied at particular locations on the display  50  corresponding to pixels in response to the stored image whereby the array of bottom electrodes  280  produce the image in the display corresponding to the stored image. 
     FIG. 6 shows a cross sectional view of a portion of an alternate embodiment of the display  50  of FIG.  1 . The cross section shows a small portion of the display. The display  50  is comprised of a substrate  240 , a heater  270  disposed on the substrate  240 , a passivation layer  260  is disposed above the heater  270 , an array of bottom electrodes  280  disposed above the passivation layer  260 , a yellow image-forming layer  120  disposed above the array of bottom electrodes  280 , a magenta image-forming layer  110  disposed above the yellow image-forming layer  120 , a cyan image-forming layer  100  disposed above the magenta image-forming layer  110 , a top electrode  290  disposed above the magenta image-forming layer, a polymer film  230  disposed above the top electrode  290 , and a protective top coat  250  disposed over the polymer film  230 . A back light  500  illuminates the display  50 . Careful comparison will reveal that the sole difference between this embodiment and the embodiment of FIG. 2 is the removal of the reflective layer  300  and corresponding addition of the back light  500 . This display is intended for back lit operation. The image-forming layer absorb light from the back light  500  to form the image which is viewed through the protective top coat  250 . The back light is driven by drive electronics  30  of FIG.  1 . 
     FIG. 7 shows a cross sectional view of a portion of a receiver according to the present invention. The cross section shows a small portion of the receiver  55 . The receiver  55  is comprised of a substrate  240 , a reflective layer  300  disposed on the substrate  240 , a yellow image-forming layer  120  disposed above the reflective layer  300 , a magenta image-forming layer  110  disposed above the yellow image-forming layer  120 , a cyan image-forming layer  100  disposed above the magenta image-forming layer  110 , and a protective top coat  250  disposed over the cyan image-forming layer. This receiver  55  is constructed in identical manner to the display  50  of FIG. 1 with the exception of the removal of the electronics. The receiver  55  functions in an identical manner to the mentioned display except the heat source and electric field are provided by an external image-forming apparatus. Such an apparatus is disclosed in commonly assigned U.S. patent application Ser. No. 09/034,066 filed Mar. 3, 1998, entitled “Printing Continuous Tone Images on Receivers Having Field-Driven Particles” to Wen et al, the disclosure of which is incorporated herein. 
     FIG. 8 shows a cross sectional view of a portion of a alternate embodiment of receiver  55  of FIG.  7 . The cross section shows a small portion of the receiver  55 . The receiver  55  is comprised of a substrate  240 , a yellow image-forming layer  120  disposed above the substrate  240 , a magenta image-forming layer  110  disposed above the yellow image-forming layer  120 , a cyan image-forming layer  100  disposed above the magenta image-forming layer  110 , and a protective top coat  250  disposed over the cyan image-forming layer. This receiver  55  is identical to the receiver of FIG. 7 with the exception of the removal of the reflective layer  300  of FIG.  7 . This receiver is intended to be display in a projection box in front of a back light  500 , shown for reference. 
     It is understood that the reflective layer  300  in FIG.  2  and FIG. 7 may be replaced with a trans-reflective layer to provide a display  50  and receiver  55  respectively capable of being back lighted or viewed reflectively. This change will not substantially alter the present invention. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                               10 
                 electronic display apparatus 
               
               
                   
                 20 
                 processing unit 
               
               
                   
                 30 
                 drive electronics 
               
               
                   
                 40 
                 heater control unit 
               
               
                   
                 50 
                 display 
               
               
                   
                 55 
                 receiver 
               
               
                   
                 60 
                 sensor 
               
               
                   
                 100 
                 cyan image-forming layer 
               
               
                   
                 110 
                 magenta image-forming layer 
               
               
                   
                 120 
                 yellow image-forming layer 
               
               
                   
                 200 
                 particle 
               
               
                   
                 210 
                 thermomeltable material 
               
               
                   
                 220 
                 constricting screen 
               
               
                   
                 225 
                 cavity 
               
               
                   
                 225A 
                 wider portion 
               
               
                   
                 225B 
                 restricted portion 
               
               
                   
                 230 
                 polymer film 
               
               
                   
                 240 
                 substrate 
               
               
                   
                 250 
                 protective top coat 
               
               
                   
                 260 
                 passivation layer 
               
               
                   
                 270 
                 heater 
               
               
                   
                 280 
                 array of bottom electrodes 
               
               
                   
                 290 
                 top electrodes 
               
               
                   
                 300 
                 reflective layer 
               
               
                   
                 401 
                 heat display 
               
               
                   
                 402 
                 write cyan plane 
               
               
                   
                 403 
                 stabilize cyan plane 
               
               
                   
                 411 
                 heat display 
               
               
                   
                 412 
                 write magenta plane 
               
               
                   
                 413 
                 stabilize magenta plane 
               
               
                   
                 421 
                 heat display 
               
               
                   
                 422 
                 write yellow plane 
               
               
                   
                 423 
                 stabilize yellow plane 
               
               
                   
                 500 
                 back light