Abstract:
A portable electronics device ( 110, 210 ) having a self illuminating display ( 112, 200, 400, 402, 404, 406, 500, 600, 700 ) that reduces both the thickness of known displays and processing steps in the fabrication thereof is provided. The portable electronic device ( 110, 210 ) includes an electrowetting display ( 112, 200, 400, 402, 404, 406, 500, 600, 700 ) having a plurality of layers ( 416, 420; 222, 210; 322, 312; 722, 712 ) defining a cavity ( 419 ) containing a mixture of a first fluid ( 418, 536, 736 ) and a second fluid ( 410, 560, 660, 730 ) positioned in the cavity ( 419 ). First circuitry ( 424 ) is configured to be coupled to a first voltage source ( 422 ) for selectively repositioning the second fluid ( 410, 560, 660, 730 ) in relation to the first fluid ( 418, 536, 736 ). A first plurality of electroluminescent particles ( 408, 560, 660, 760 ) are positioned within the second fluid ( 410, 560, 660, 730 ), and second circuitry ( 428 ) is configured to be coupled to a second voltage source ( 426 ) for selectively causing the electroluminescent particles ( 408, 560, 660, 760 ) to emit photons ( 430 ). Additional similar stacks of layers ( 504, 506, 604, 606 ) may be added to provide a color display.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to portable electronic devices and more particularly to a portable electronic device having a self illuminating display. 
       BACKGROUND OF THE INVENTION 
       [0002]    The market for personal portable electronic devices, for example, cell phones, personal digital assistants (PDA&#39;s), digital cameras, and music playback devices (MP3), is very competitive. Manufactures are constantly improving their product with each model in an attempt to cut costs and to meet production requirements. 
         [0003]    In many portable electronic devices, such as mobile communication devices, displays present information to a user. For example, electrowetting display technology can display video and text information. This low cost reflective display technology comprising electrowetting light valves, may be used to produce stacked black and white, or colored, shutters over a reflective surface. Typical electrowetting devices use a DC voltage to change the wetting properties between a solid and a liquid, thereby moving the colored oil like a shutter in and out of view. Color electrowetting schemes use absorptive oils of Cyan, Magenta, and Yellow for the highest efficiency subtractive approach. The ‘open’ condition of the shutter is transparent (not black or white) so that the underlying colors are visible when the first color is “off”. 
         [0004]    These reflective displays are built above a reflective surface that reflects ambient light through the device to illuminate the oil or lack thereof. When ambient light is insufficient, the displays are difficult to see. Conventional liquid crystal displays have included a backlight that provides a white light vertically through the display, through the oil or lack thereof, to be viewed by the user. However, this backlight requires additional layers adjacent each pixel in the display and several additional process steps in the fabrication thereof. 
         [0005]    Accordingly, it is desirable to provide a portable electronics device having a self illuminating display that reduces both the thickness of known displays and processing steps in the fabrication thereof. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A portable electronic device having a self illuminating display that reduces both the thickness of known displays and processing steps in the fabrication thereof is provided. The portable electronic device includes an electrowetting display having a plurality of layers defining a cavity containing a combination of a first fluid and a second fluid positioned in the cavity. First circuitry is configured to be coupled to a first voltage source for selectively repositioning the second fluid in relation to the first fluid. A plurality of electroluminescent particles is positioned within the second fluid; and second circuitry configured to be coupled to a second voltage source selectively causes the electroluminescent particles to emit light. Additional similar plurality of layers may be added to provide a color display. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0008]      FIG. 1  is a front view of a portable electronic device including a display suitable for use with the exemplary embodiment; 
           [0009]      FIG. 2  is a block diagram illustrating circuitry for implementing various exemplary embodiments on the portable electronic device of  FIG. 1 ; 
           [0010]      FIG. 3  is a schematic partial cross section illustrating a previously known pixel of an electrowetting display; 
           [0011]      FIGS. 4-7  are schematic partial cross sections illustrating four operational states for an exemplary embodiment; 
           [0012]      FIG. 8  is a partial cross section of a second exemplary embodiment; 
           [0013]      FIG. 9  is a partial cross section of a third exemplary embodiment; and 
           [0014]      FIG. 10  is a partial cross section of a fourth exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
         [0016]    Referring to  FIG. 1 , a portable electronic device  110  comprises a display  112 , a control panel  114 , and a speaker  116  encased in a housing  120 . Some portable electronic devices  110 , e.g., a cell phone, may include other elements such as an antenna, a microphone, and a camera (none shown). In the exemplary embodiments described herein, the display  112  comprises a reflective electrowetting technology. The exemplary embodiment may comprise any type of electronic device, for example, a PDA, a mobile communication device, and gaming devices. 
         [0017]    Referring to  FIG. 2 , a block diagram of a portable electronic device  210  such as a cellular phone, in accordance with the exemplary embodiment is depicted. Though the exemplary embodiment is a cellular phone, the display described herein may be used with any electronic device in which information, colors, or patterns are to be presented. The portable electronic device  210  includes an antenna  212  for receiving and transmitting radio frequency (RF) signals. A receive/transmit switch  214  selectively couples the antenna  212  to receiver circuitry  216  and transmitter circuitry  218  in a manner familiar to those skilled in the art. The receiver circuitry  216  demodulates and decodes the RF signals to derive information therefrom and is coupled to a controller  220  for providing the decoded information thereto for utilization thereby in accordance with the function(s) of the portable communication device  210 . The controller  220  also provides information to the transmitter circuitry  218  for encoding and modulating information into RF signals for transmission from the antenna  212 . As is well-known in the art, the controller  220  is typically coupled to a memory device  222  and a user interface  114  to perform the functions of the portable electronic device  210 . Power control circuitry  226  is coupled to the components of the portable communication device  210 , such as the controller  220 , the receiver circuitry  216 , the transmitter circuitry  218  and/or the user interface  114 , to provide appropriate operational voltage and current to those components. The user interface  114  includes a microphone  228 , a speaker  116  and one or more key inputs  232 , including a keypad. The user interface  114  may also include a display  112  which could include touch screen inputs. The display  112  is coupled to the controller  220  by the conductor  236  for selective application of voltages in some of the exemplary embodiments described below. 
         [0018]    The exemplary embodiments described herein may be fabricated using known lithographic processes as follows. The fabrication of integrated circuits, microelectronic devices, micro electro mechanical devices, microfluidic devices, and photonic devices, involves the creation of several layers of materials that interact in some fashion. One or more of these layers may be patterned so various regions of the layer have different electrical or other characteristics, which may be interconnected within the layer or to other layers to create electrical components and circuits. These regions may be created by selectively introducing or removing various materials. The patterns that define such regions are often created by lithographic processes. For example, a layer of photoresist material is applied onto a layer overlying a wafer substrate. A photomask (containing clear and opaque areas) is used to selectively expose this photoresist material by a form of radiation, such as ultraviolet light, electrons, or x-rays. Either the photoresist material exposed to the radiation, or that not exposed to the radiation, is removed by the application of a developer. An etch may then be applied to the layer not protected by the remaining resist, and when the resist is removed, the layer overlying the substrate is patterned. Alternatively, an additive process could also be used, e.g., building a structure using the photoresist as a template. 
         [0019]    Though the above described lithography processes are preferred, other fabrication processes may comprise any form of lithography, for example, ink jet printing, photolithography, electron beam lithography, and imprint lithography ink jet printing. In the ink jet printing process, the EL particles are combined in liquid form with the oil and printed in desired locations on the substrate. 
         [0020]    A low cost reflective display technology, electrowetting light valves, may be used to produce stacked black and white, or colored, shutters over a reflective surface. Typical electrowetting devices use a low frequency voltage, including DC, to change the wetting properties of a drop of oil in water, thereby moving the colored oil like a shutter in and out of view. Color electrowetting schemes typically use absorptive oils of Cyan, Magenta, and Yellow for the highest efficiency subtractive approach. The ‘open’ condition of the shutter is transparent (not black or white) so that the underlying colors are visible when the first color is “off”. 
         [0021]      FIG. 3  is partial cross section of a known electrowetting display  300  of a single pixel comprising a reflective material  311  deposited on a substrate  312  and a transparent electrode  314  is formed on the reflective material  311 . A transparent hydrophobic insulator  316  is formed on the electrode  314  for supporting the combination of oil  310  and water  318 . A transparent electrode  320  is formed above and for containing the water  318  and oil  310  in a cavity  319 . A DC/low frequency voltage source  322 , e.g., DC to 200 hertz, is coupled between the electrodes  314  and  320 , and is selectively applied by closing the switch  324 . When the switch  324  is closed and a voltage is applied across the conductors  314  and  320 , the oil  310  moves to the side (not shown) as is known in the industry by being displaced against the transparent hydrophobic insulator  316  by the water  318 . 
         [0022]    In operation, without voltage applied, the layer of absorptive oil  310  is located in the optical path, and a color is displayed. By applying a DC, or low frequency, voltage to the layers (typically &lt;40 V), the oil  310  moves to the side of each cell, eliminating the absorption of the light. Incident light then bounces off the reflective surface  311  and back to the viewer. The amount of displacement of the oil is correlated to the applied voltage. Consequently, different shades (greyscales) are obtained by modulating the applied voltage level. The color is maintained by continual application of applied voltage. However, the leakage current is tremendously small, and shades can be maintained for minutes after the voltage source  322  is disconnected. In the illustrated known display, voltage levels are applied to the display  300  once to set the desired color, and then they are re-applied at intervals (for example, 2 minutes), to refresh the charge. 
         [0023]    In accordance with the exemplary embodiment, electroluminescent (EL) particles are distributed within the oil. The EL particles preferably comprise a semiconductor compound, for example, a II-VI compound such as zinc sulfide, but may comprise other materials, for example, a dopant such as copper. The EL particles may be mixed in solution with the oil before being placed within the display. 
         [0024]    An AC voltage is selectively applied across the oil containing the EL particles, causing the particles to emit light when the AC voltage is applied. In good lighting conditions, the ambient light reflected through the display may be sufficient and the AC voltage need not be applied. However, when ambient lighting is insufficient, the AC voltage may be applied across the oil causing the EL particles to provide sufficient light for viewing the information presented thereon. The electrons in EL particles are excited by the AC voltage and released their energy as photons when combined with holes. This electrowetting technology uses low cost materials and low cost driving methods. 
         [0025]      FIGS. 4-7  are schematic diagrams of four states of a single level in which an electrowetting display  400 ,  402 ,  404 ,  406 , respectively, includes electroluminescent particles  408  disposed within the oil  410 . Each of the  FIGS. 4-7  comprise a reflective electrode  414  deposited on a substrate  412 . A transparent hydrophobic insulator  416  is formed on the electrode  414  for supporting the combination of oil  410  and water  418 . A transparent electrode  420  is formed above and for containing the water  418  and oil  410  in a cavity  419 . A first (low frequency or DC) voltage source  422  is coupled between the electrodes  414  and  420 , and is selectively applied by closing the first switch  424 . A second (AC) voltage source  426 , preferably in the range of 400 to 1600 hertz, is coupled between the electrodes  414  and  420  in parallel with the first voltage source  422 , and is selectively applied by closing the second switch  426 . The low frequency voltage from the first voltage source preferably comprises a frequency of DC to less than 200 hertz and is preferably about 400 hertz less than the voltage from the second voltage source  426 . 
         [0026]      FIG. 4  shows the switches  424  and  428  open, resulting in the oil being dispersed across the hydrophobic insulator  416  and in the EL particles  408  being non-luminescent. This state is selected to display the color of the oil  410  when ambient conditions are sufficient to provide lighting from the reflective electrode  414 . 
         [0027]      FIG. 5  shows the switch  424  closed and the switch  428  open, resulting in the oil being pulled to the side of the hydrophobic insulator  416  and the EL particles  408  being non-luminescent. This state is selected to not display the color (or white for a non-color display) of the oil  410  when ambient conditions are sufficient to provide lighting from the reflective electrode  414 . 
         [0028]      FIG. 6  shows the switch  424  open and the switch  428  closed, resulting in the oil being dispersed across the hydrophobic insulator  416  and the EL particles  408  being luminescent. This state is selected to display the color of the oil  410  when ambient conditions are insufficient to provide lighting from the reflective electrode  414 . Photons  430  emitted from the EL particles  408  provide lighting for the display  404 . 
         [0029]      FIG. 7  shows the switches  424  and  428  closed, resulting in the oil  410  being pulled to the side of the hydrophobic insulator  416  and the EL particles  408  being luminescent. This state is selected to display the color shade or grayscale of the oil  410  when ambient conditions are insufficient to provide lighting from the reflective electrode  414 . The EL particles  408  provide lighting, photons  430 , for the display  404 . 
         [0030]    The DC or low frequency voltage from the first voltage source  422  may be varied (by replacing switch  424  with a variable switch), resulting in a variable amount of the oil  410  covering the hydrophobic insulator  416 , and therefore, resulting of shades of color in a color display or a gray scale in a black and white display. 
         [0031]    Colored electrowetting technology, in preferred embodiments, uses a colored shutter (color by absorption rather than reflection), which allows layers to be stacked to form an efficient reflective surface. The “open shutter” transmissivity may exceed 80 to 90% for each tier. Three exemplary embodiments of a color display are described below with reference to  FIGS. 8-10 . 
         [0032]    Referring to  FIG. 8 , a color display  500  comprises three tiers  502 ,  504 ,  506 . Each tier is an independent color cell, and these tiers  502 ,  504 ,  506  are fastened together. One method of fastening is an index-matched optical adhesive. Each tier  502 ,  504 ,  506  contains a top substrate  510 ,  510 ′,  510 ″, respectively, and a bottom substrate  508 ,  508 ′,  508 ″, respectively. Similar elements are identified with a number in tier  502 , a prime of the number in the tier  504 , and a double prime in the tier  506 . In the preferred embodiment, all six substrate layers  508 ,  510 ,  508 ′,  510 ′,  508 ″,  510 ″ are formed of a transparent, sturdy, thin material such as glass, but preferably would comprise a flexible polymer such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). A white reflective backplane  512  is positioned at the bottom of the substrate  508 . Alternatively, the bottom substrate  508  of tier  502  may be replaced with a compatible white substrate, thereby omitting the bottom layer  512 . The tier  502  comprises transparent conductor  516 , for example, indium tin oxide (ITO) or poly-3,4-ethylenedioxythiophene (PEDOT), deposited on substrate  508 . An optional insulator material  518  is deposited over the conductor  516  and substrate  508 . A layer  522  of a hydrophobic (insulator) film is formed on the optional insulator material  518  (or the conductor  516 ). The layer  522  comprises, for example, fluoropolymers and parylene. A material  524  is patterned on the surface  526  of the layer  522  to establish an operating element size. The pattern of the material  524  preferably forms a grid of ribs which creates an array of cells,  532 , but may take any form. Although three cells  532  are shown, it should be understood a large plurality of cells  532  may be fabricated. In a preferred embodiment, the grid is formed from polymethyl methacrylate (PMMA), a photoresist such as epoxy-based SU8 from Microchem, or by hot embossing. A first oil  534  is placed on the surface  526  of the material  524  within the voids  532 . The first oil  534  comprises, for example, a mineral oil containing pigments which are soluble in oil, but not water. Example pigments or chromophores are commercially available as dyes, including Cyan, Magenta, and Yellow, at a small weight percent concentration. Another example of pigments or chromophores include lithol rubine (Red), B: copper thalocyanine (Blue), diarylide yellow (Yellow) at 4 weight percent concentration. The rest of the cell is filled with a fluid that does not mix with oil, for example, water. The fluid  536  may contain surfactants and other elements to extend the temperature range of the fluid, aid manufacturing, and improve oil repulsion. The fluid  536  is placed on the first oil  534  and sealed in place by the combination of the seal  538  and the substrate  510 . An electrode  540  comprising a transparent conductive material such as indium tin oxide is formed on the substrate  510  for contacting the fluid  536 . In another embodiment, this electrode  540  may be patterned, for example, to include bus lines. 
         [0033]    The second tier  504  and third tier  506  are fabricated similar to the first tier  502 , with like elements represented by the same number, except those in the second tier  504  are identified with a single prime (′) and those in the third tier  506  are identified with a double prime (″). A difference in the tiers  502 ,  504 ,  506  is that the second tier  504  comprises a second oil  544  and the third tier  506  comprises a third oil  554 . Though the color of the oils  534 ,  544 ,  554  in the tiers  502 ,  504 ,  506  may be in any order, preferably the first, second, and third oils  534 ,  544 ,  554  comprise red, blue, and green, or cyan, magenta, and yellow. 
         [0034]    Electroluminescent (EL) particles  560  are distributed within the oil  534 ,  544 , and  554 . An AC voltage (as described with reference to  FIGS. 4-7 ) is selectively applied across the oil  534 ,  544 ,  554  containing the EL particles  560 , causing the particles to emit sufficient light for viewing the information presented on the display  500 . 
         [0035]    For displaying a simple color, an electrical connection is needed for the ground planes in each cell, and for the three color layers. The entire display functions as a single pixel. The display surface may be subdivided into regions with various shapes to permit different areas to display different colors or information. The additional electrical connections require additional interconnects and driving electronics. 
         [0036]    In operation, when a desired color and/or pattern (including information such as text) is determined, signals are sent to each tier  502 ,  504 ,  506  to move none, one, two, or three of the oils  534 ,  544 ,  554 . When one of the oils, e.g.,  534 , is selected to open, the voltage applied across the tier  502  causes the oil to withdraw to a corner of its void  532 , allowing light to bypass the oil  534 . Therefore, by applying the proper signals to each of the tiers  502 ,  504 ,  506 , the desired color is achieved. 
         [0037]    Without voltage applied, three layers of absorptive oils are located in the optical path, and the display looks black (for the cyna-magenta-yellow subtractive approach). By applying a DC, or a low frequency, voltage to the layers (typically &lt;40 V), the colored oil moves to the side of each cell, eliminating the absorption of specific wavelengths. Incident light then bounces off the backplane and reflect back to the viewer. The amount of displacement of the colored oil is correlated to the applied voltage. Consequently, different shades of colors (greyscales) are obtained by modulating the applied voltage level. The color is maintained by continual application of applied voltage. However, the leakage current is tremendously small, and colors can be maintained for minutes after a voltage source is disconnected. In a preferred embodiment, voltage levels are applied to the display once to set the desired color, and then they are re-applied at intervals (for example, 2 minutes), to refresh the charge. 
         [0038]    A second exemplary electrowetting technology embodiment of a color display  600  for a portable electronic device  110  is shown in  FIG. 9  wherein elements similar to those of  FIG. 8  comprise similar material composition. The display  600  comprises three tiers  602 ,  604 ,  606 , except the second and third tiers  604 ,  606  are inverted from those of the exemplary embodiment of  FIG. 8  to reduce the number of layers, the number of process steps, the overall thickness, and the optical efficiency. The tier  602  is formed between the substrate  608  and the second tier  604 , the tier  604  is formed between the tier  602  and the substrate  610 ′, and the tier  606  is formed between the substrate  610 ′ and  610 ″. A white reflective backplane  612  is positioned at the bottom of the substrate  608 . Alternatively, the bottom substrate  608  of tier  602  may be replaced with a compatible white substrate, thereby omitting the bottom layer  612 . The tier  602  comprises a transparent conductor  616 , for example, indium tin oxide (ITO) or poly-3,4-ethylenedioxythiophene (PEDOT), patterned on the substrate  708 . An optional insulator material  618  is deposited on the oxide  614  and conductor  616 . A layer  622  of a hydrophobic (insulator) film is formed on the optional insulator material  618  (or alternatively on the oxide  614  and conductor  616 ). A material  624 , e.g., a dielectric, is patterned on the surface  626  of the layer  622  to define cells  632 . The pattern of the material  624  preferably forms a grid, creating an array of cells  632 , but may take any form. A first oil  634  is placed on the surface  626  of the material  624  within the voids  632 . The hydrophobic material comprises, for example, SU8 photoresist, that repulses the fluid  636 . The fluid  634  is placed on the first oil  634  and sealed in place by the combination of the seal  638  and the substrate  610 . An electrode  640  comprising a transparent conductive material such as indium tin oxide is formed on the seal  638  for contacting the fluid  636 . 
         [0039]    The second tier  604  and third tier  606  are fabricated similar to the first tier  602  but inverted to that of the first tier  602 , with like elements represented by the same number, except those in the second tier  604  are identified with a single prime (′) and those in the third tier  606  are identified with a double prime (″). A difference in the tiers  602 ,  604 ,  606  is that the second tier  604  comprises a second oil  644  and the third tier  606  comprises a third oil  654 . Though the color of the oils  634 ,  644 ,  654  in the tiers  602 ,  604 ,  606  may be in any order, preferably the first, second, and third oils  634 ,  644 ,  654 , respectively, comprise red, blue, and green, or cyan, magenta, and yellow. An electrode  642 ″ is provided for coupling to the fluid  636 ″. 
         [0040]    Electroluminescent (EL) particles  660  are distributed within the oil  634 ,  644 , and  654 . An AC voltage (as described with reference to  FIGS. 4-7 ) is selectively applied across the oil  634 ,  644 ,  654  containing the EL particles  660 , causing the particles to emit sufficient light for viewing the information presented on the display  600 . El particles can be selected to have a narrow spectrum range to match the color of the oil or have a wider spectrum range (for example white light) with the color oil filtering out unwanted colors. 
         [0041]    For displaying a simple color, an electrical connection is needed for the ground planes in each cell, and for the three color layers. The entire display functions as a single pixel. The display surface may be subdivided into regions with various shapes to permit different areas to display different colors or information. The additional electrical connections require additional interconnects and driving electronics. 
         [0042]    In operation, when a desired color and/or pattern (including information such as text) is determined, signals are sent to each tier  602 ,  604 ,  606  to move none, one, two, or three of the oils  634 ,  644 ,  654 . When one of the oils, e.g.,  634 , is selected to open, the voltage applied across the tier  602  causes the oil to withdraw to a corner of its void  632 , allowing light to bypass the oil  634 . Therefore, by applying the proper signals to each of the tiers  602 ,  604 ,  606 , the desired color is achieved. 
         [0043]    Without voltage applied, three layers of absorptive oils are located in the optical path, and the display looks black (for the cyna-magenta-yellow subtractive approach). By applying a DC, or a low frequency, voltage to the layers (typically &lt;40 V), the colored oil moves to the side of each cell, eliminating the absorption of specific wavelengths. Incident light then bounces off the backplane and back to the viewer. The amount of displacement of the colored oil is correlated to the applied voltage. Consequently, different shades of colors (greyscales) are obtained by modulating the applied voltage level. The color is maintained by continual application of applied voltage. However, the leakage current is tremendously small, and colors can be maintained for minutes after a voltage source is disconnected. In a preferred embodiment, voltage levels are applied to the display once to set the desired color, and then they are re-applied at intervals (for example, 2 minutes), to refresh the charge. 
         [0044]      FIG. 10  is a third exemplary embodiment of a color display  700  for a portable electronic device  110  wherein elements similar to those of  FIG. 9  comprise similar material composition. The display  700  comprises four tiers  701 ,  702 ,  704 ,  706 , except the second and third tiers  704 ,  706  are inverted from those of the exemplary embodiment of  FIG. 9 . Tiers  701  and  702  may be used for a one color device, and tiers  704  and  706  may be optionally added for a three color device. The tier  701  is formed between the substrate  712  and the second tier  702 , the tier  702  is formed between the tier  701  and the third tier  704 , the tier  704  is formed between the tier  702  and the fourth tier  706 , and the tier  706  is formed between the tier  704  and the substrate  708 ″. A white reflective backplane  712  is positioned at the bottom of the substrate  708 . Alternatively, the bottom substrate  708  of tier  701  may be replaced with a compatible white substrate, thereby omitting the bottom layer  712 . 
         [0045]    The fabrication of the tiers  701 ,  702 , and  704 ,  706  is similar to the fabrication of the tiers  602 ,  604  in  FIG. 9 . The tier  701  comprises a transparent conductor  716 , for example, indium tin oxide (ITO) or poly-3,4-ethylenedioxythiophene (PEDOT), patterned on the substrate  708 . An optional insulator material ( 718 ) is deposited on the oxide  714  and conductor  716 . A layer  722  of an insulator film is formed on the optional insulator material (or alternatively on the oxide  714  and conductor  716 ). A hydrophobic material  724  is patterned on the surface  726  of the layer  722 . The pattern of the material  724  preferably forms a grid, creating an array of cells  732 , but may take any form. A first oil  730  is placed on the surface  726  of the material  722  within the voids  732  created by the material  724 . The hydrophobic material comprises, for example, teflon® AF2400 solution, that repulses the fluid  736 . The fluid  736  is placed on the first oil  730  and sealed in place by the combination of the seal  738  and the second tier  702 . An electrode  740  comprising a transparent conductive material such as indium tin oxide is formed on the seal  738  for contacting the fluid  736 . 
         [0046]    The second, third, and fourth tiers  702 ,  704 ,  706  are fabricated similar to the first tier  701 , with like elements represented by the same number, except those in the second tier  702  are identified with a single prime (′), those in the third tier  706  are identified with a double prime (″), and those in the fourth tier are identified with a triple prime (′″). The first and second tiers  701 ,  702 , and third and fourth tiers  704 ,  706 , respectively, are fabricated in pairs. A difference in the tiers  701 ,  702 ,  704 ,  706  is that the first tier  701  comprises a first oil containing EL particles  760 , the second tier  702  comprises a first color oil  734 , the third tier  704  comprises a second color oil  744 , and the fourth tier  706  comprises a third color oil  754 . Though the color of the oils  734 ,  744 ,  754  in the tiers  702 ,  704 ,  706  may be in any order, preferably the first, second, and third oils  734 ,  744 ,  754 , respectively, comprise red, blue, and green, or cyan, magenta, and yellow. 
         [0047]    Electroluminescent (EL) particles  760  are distributed within the oil  730 . An AC voltage is selectively applied (as described with reference to  FIGS. 4-7 ) across the oil  730  containing the EL particles  760 , causing the particles to emit light sufficient light for viewing the information presented on the display  700 . 
         [0048]    For displaying a simple color, an electrical connection is needed for the ground planes in each cell, and for the three color layers. The entire display functions as a single pixel. The display surface may be subdivided into regions with various shapes to permit different areas to display different colors or information. The additional electrical connections require additional interconnects and driving electronics. 
         [0049]    In operation, when a desired color and/or pattern (including information such as text) is determined, signals are sent to each tier  702 ,  704 ,  706  to move none, one, two, or three of the oils  734 ,  744 ,  754 . When one of the oils, e.g.,  734 , is selected to open, the voltage applied across the tier  702  causes the oil to withdraw to a corner of its void  732 , allowing light to bypass the oil  734 . Therefore, by applying the proper signals to each of the tiers  702 ,  704 ,  706 , the desired color is achieved. 
         [0050]    Without voltage applied, three layers of absorptive oils are located in the optical path, and the display looks black (for the cyna-magenta-yellow subtractive approach). By applying a DC, or a low frequency, voltage to the layers (typically &lt;40 V), the colored oil moves to the side of each cell, eliminating the absorption of specific wavelengths. Incident light then bounces off the backplane and back to the viewer. The amount of displacement of the colored oil is correlated to the applied voltage. Consequently, different shades of colors (greyscales) are obtained by modulating the applied voltage level. The color is maintained by continual application of applied voltage. However, the leakage current is tremendously small, and colors can be maintained for minutes after a voltage source is disconnected. In a preferred embodiment, voltage levels are applied to the display once to set the desired color, and then they are re-applied at intervals (for example, 2 minutes), to refresh the charge. 
         [0051]    In any of the embodiments, including the exemplary embodiments described herein, the EL particles  408 ,  560 ,  660 ,  760  may be fabricated to emit light at a desired frequency, thereby imparting a desired color. El particles  408 ,  560 ,  660 ,  760  are fabricated from, for example, a II-IV semiconductor compound having direct band gaps for efficient electroluminescence. The bank gap can be shifted by the presence of impurities or dopants. The selection of dopant in the compound will permit the EL to emit light with a specific color or a white light. This color emitted from the EL particles results in that color being emitted from single cell displays such as shown in  FIGS. 4-7 . This color emitted from the EL particles may be combined with the colored light provided by the multiple stacked layers such as shown in  FIGS. 8-10 . 
         [0052]    Additionally, quantum dots may be used instead of the EL particles. Quantum dots emit photons having a frequency depending on the material selected for, and the size of, the quantum dot. Quantum dots comprise an inorganic nanocrystal material, for example, PbSe, CdSe, (CdSe)ZnS, Au, having a diameter, for example, in the range of 3-10 nanometers. Quantum dots may be excited by the application of the AC voltage described herein. This color emitted from the quantum dots results in that color being emitted from single cell displays such as shown in  FIGS. 4-7  when the oil color is clear. This color emitted from the quantum dots may be combined with the colored light provided by the multiple stacked layers such as shown in  FIGS. 8-10 . 
         [0053]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.