Abstract:
A bistable electrowetting picture element that has both stable “On” and “Off” states in which no power is consumed, and a switching voltage threshold. Displays using such picture elements may be either passive or active matrix addressed. A picture element contains two immiscible, fluids within a space between two surfaces. One of the fluids is an electroconductive, polar liquid, such as to water. The other fluid is a non-polar liquid such as silicone oil. The picture element is electrically switchable between two states, both of which are maintained without a voltage being applied. In one state the light absorbing, non-polar liquid adjoins a region of one of the surfaces, while in the second state it adjoins another region on the other surface. The region adjoined to in the second state differs in area from the region adjoined to in the first state, thereby providing “On” and “Off” states.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to, and claims priority from, U.S. Provisional Patent application No. 60/893,669 filed on Mar. 8, 2007 by R. Rosser, the contents of which are hereby incorporated by reference. This application is also related to U.S. Provisional Patent applications No. 60/894,210 filed on Mar. 10, 2007, No. 60/908,103 filed on Mar. 26, 2007, No. 60/939,061 filed on May 19, 2007, No. 60/943,752 filed on Jun. 13, 2007 and No. 61/016,750 filed on Dec. 26, 2007, the contents of all of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of electrowetting displays. More specifically, the present invention relates to a method, apparatus, and system for bistable, electrowetting picture elements and displays. 
     BACKGROUND OF THE INVENTION 
     In the $20 billion mobile display market, the dominant display technology is liquid crystal (LCD) technology. This dominance may be measured by the fact that in 2006, of the 1 billion plus displays that were shipped for mobile devices, such as cellular phones, over 95% used LCD technology. 
     Despite their present dominance, LCD displays have the drawback of requiring back-lighting that can be very power consuming. This is of particular concern in battery operated, mobile devices such as cellular phones. In a typical cellular phone, back-lighting consumes about 80% of the battery power required to operate the phone. 
     Because of this drawback, there is considerable interest in alternative display technologies, particularly reflective display technologies that make use of ambient light rather than requiring backlighting. One alternative, reflective display technology that has received considerable attention is electrowetting display technology. 
     Electrowetting display technology uses the well-known electrowetting effect, in which the wetting properties of a surface can be altered by applying a voltage, to manipulate a colored oil from covering an entire picture element to beading up to cover only a small fraction of the picture element. When the oil covers the entire picture element, all the light is absorbed by the dye coloring the oil and the picture element is in an “Off” state. When the oil covers only a portion of the picture element, light can be transmitted—or reflected—by the picture element and it is in an “On” state. Reflective electrowetting displays may be made in which no light is reflected in the “Off” state and about 65% of the incident light is reflected in the “On” state. This compares to paper in which white paper reflects about 70% of the incident light, while black ink reflects almost none. 
     Electrowetting display technology has been described in detail in, for instance, US Patent publications no. 20050270672 by Feenstra et al. (Dec. 8, 2005), no. 20050213014 by Feenstra et al. (Sep. 29, 2005), no. 20050104804 by Feenstra et al. (May 19, 2005) no. 20060132404 by Hayes et al. (Jun. 22, 2006), no. 20050123243 Steckl et al. (Jun. 9, 2005) no. 20070031097 by Heikenfeld et al. (Feb. 8, 2007) the contents of all of which are hereby incorporated by reference. 
       FIGS. 1A and 1B  show various components of an exemplary embodiment of prior art electrowetting display technology. A prior art, electrowetting picture element  10  typically has two immiscible fluids contained between an upper, hydrophilic surface  16  and a lower, hydrophobic surface  18 . The immiscible fluids are typically a non-polar liquid  12 , such as oil, and a polar liquid  14 , such as water. The non-polar liquid  12  typically has added dyes or pigments to facilitate absorbing some, or all, of the incident light. 
     In an “Off” state, shown in  FIG. 1A , the non-polar liquid  12  completely covers the hydrophobic surface  18  of the electrowetting picture element  10 . In this “Off” state, incident light  22  is absorbed by the non-polar liquid  12  and any added dyes or pigments it may contain. 
     An “On” state of the prior art, electrowetting picture element  10  is achieved by applying a suitable voltage  24  between a transparent electrode  20  and the polar liquid  14 . The transparent electrode  20  is electrically isolated from the polar liquid  14  by the hydrophobic surface  18  that is also a dielectric. The polar liquid  14  may have additives such as, but not limited to, acids, alkalis or salts or a combination thereof, to make the polar liquid  14  more conductive to electricity. The application of a suitable voltage  24  to such an arrangement results in the well-know electrowetting phenomenon in which the surface  18  becomes less hydrophobic. As surface  18  becomes less hydrophobic, the non-polar liquid  12  beads up, allowing the polar liquid  14  to come into contact with surface  18 . As a result, some of the incident light  22  is no longer blocked by the non-polar liquid  12  and now emerges from the prior art, electrowetting picture element  10  as emergent light  26 . 
     A significant draw back of the prior art, electrowetting picture element elements  10  are that they require a small, but continuous, voltage to be applied to maintain an “On” state. This means that when they are displaying an image, they are consuming power. 
     For many applications, including e-books, e-signage and mobile device displays, it is desirable to have both an “On” state as well as an “Off” state that require no power. Such a display element is typically termed a “bistable” display element. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a bistable electrowetting picture element that may be suitable for use in a display. The bistable, electrowetting picture element of this invention has both a stable “On” state and a stable “Off” state in which no power is consumed. In addition, the bistable, electrowetting picture element of this invention has a switching voltage threshold. As a result a display made of the electrowetting picture elements of this invention may be operated using either passive matrix addressing or active matrix addressing. 
     In a preferred embodiment, the bistable, electrowetting picture element contains two fluids that are immiscible with each other. The immiscible fluids are contained within a space between two surfaces that confront each other. One of the fluids is an electroconductive or polar liquid such as, but not limited, to water. The other fluid is a non-polar liquid such as, but not limited to, oil or silicone oil that may also contain light absorbing dyes and pigments. 
     The picture element is electrically switchable between two states, both of which are maintainable without a voltage being applied. In one state the fluid that is a non-polar liquid adjoins a region of one of the surfaces, while in the second state, the fluid that is a non-polar liquid adjoins another region on the other surface. The region adjoined to in the second state differs in area from the region adjoined to in the first state. The amount of light absorbed by the picture element is proportional to the size of the region to which the light absorbing, non-polar liquid is adjoined. If, in the first state, the region corresponds to the entire area of the picture element, no light will be transmitted and the picture element will be in an “Off” state. If in the second state the region corresponds to some fraction of the area of the picture element, some light will be transmitted and the picture element will be in an “On” state. 
     These and other features of the invention will be more fully understood by references to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic cross-section of an exemplary embodiment of a prior art electrowetting picture element in an “Off” state. 
         FIG. 1B  is a schematic cross-section of an exemplary embodiment of a prior art electrowetting picture element in an “On” state. 
         FIG. 2A  is a schematic cross-section of an exemplary transmission mode bistable, electrowetting picture element of the present invention in an “Off” state. 
         FIG. 2B  is a schematic cross-section of an exemplary transmission mode bistable, electrowetting picture element of the present invention in an “On” state. 
         FIG. 3  is a schematic cross-sectional view of an exemplary reflection mode, bistable, electrowetting picture element transitioning from an “Off” state to an “On” state and back again. 
         FIG. 4  is a schematic plan view of an exemplary bistable, electrowetting picture element transitioning from an “Off” state to an “On” state and back again. 
         FIG. 5  is a schematic cross-section of a further exemplary bistable, electrowetting picture element of the present invention in an “Off” state. 
         FIG. 6  is a schematic cross-section of a further exemplary bistable, electrowetting picture element of the present invention in an “On” state. 
         FIG. 7A  shows a hydrophilic picture element defining barrier defining a single square picture element. 
         FIG. 7B  shows a square picture element subdivided into four equal sub-picture regions. 
         FIG. 7C  shows a square picture element subdivided into nine equal sub-picture regions. 
         FIG. 7D  shows a square picture element subdivided into five equal sub-picture regions. 
         FIG. 8A  shows a schematic plan view of a picture element that has four sub-picture regions in an “On” state. 
         FIG. 8B  shows a schematic plan view of a picture element that has five sub-picture regions in an “On” state. 
         FIG. 8C  shows a schematic plan view of a picture element that has nine sub-picture regions in an “On” state. 
         FIG. 9A  shows a plan view of an exemplary picture element  60  divided into three regions of unequal area. 
         FIG. 9B  shows a plan view of an exemplary structure of a lower electrode configured to drive the picture element of  FIG. 9A . 
         FIG. 10  shows a schematic plan view of a multi-region structure. 
         FIG. 11  shows a schematic cross-sectional view of the multi-region structure of  FIG. 10 . 
         FIG. 12  shows a schematic cross-sectional view of the multi-region structure loaded with non-polar liquid. 
         FIG. 13  shows a schematic cross-sectional view of an exemplary configuration for loading a multi-region structure with non-polar liquid. 
         FIG. 14  shows a schematic cross-sectional view of a further exemplary configuration for loading a multi-region structure with non-polar liquid. 
         FIG. 15  shows a schematic cross-sectional view of an exemplary configuration for loading a roll of multi-region structure with non-polar liquid. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is innovative over the prior art in providing a simple but novel, bistable electrowetting display technology. To understand the inventive concepts of the present invention it is useful to consider the accompanying drawings in which, as far as possible, like numbers represent like elements. 
     Although every reasonable attempt is made in the accompanying drawings to represent the various elements of the embodiments in relative scale, it is not always possible to do so with the limitations of two-dimensional paper. Accordingly, in order to properly represent the relationships of various features among each other in the depicted embodiments and to properly demonstrate the invention in a reasonably simplified fashion, it is necessary at times to deviate from absolute scale in the attached drawings. However, one of ordinary skill in the art would fully appreciate and acknowledge any such scale deviations as not limiting the enablement of the disclosed embodiments. 
       FIGS. 2A and 2B  shows various components of an exemplary bistable, electrowetting display picture element  30  that can be utilized to implement the inventive concepts described herein. The bistable, electrowetting display picture element  30  includes two immiscible fluids contained between an upper, hydrophilic surface  16  and a lower, hydrophobic surface  18 . In addition, the bistable, electrowetting display picture element  30  includes a second, hydrophobic region  28  that may cover part of the hydrophilic surface  16 . The immiscible fluids may, for instance be a non-polar liquid  12 , such as oil, and a polar liquid  14  such as water. The non-polar liquid  12  may contain dyes or pigments to facilitate light absorption. The polar liquid  14  may contain salts, acids or alkalis to enhance the electrical conductivity of the liquid. The polar liquid  14  may also, or instead, contain additives such as, but not limited to, glycerol or alcohol, or some combination thereof, to allow the device to operate over more extended temperature ranges. 
     In an “Off” state of the bistable, electrowetting display picture element  30 , shown in  FIG. 2A , the non-polar liquid  12  is in contact with the lower hydrophobic surface  18  and covers the entire lower surface  18 . In the “Off” state, incident light  22  is absorbed by the non-polar liquid  12  over the entire bistable, electrowetting display picture element  30 . 
     In an “On” state of the bistable, electrowetting display picture element  30 , shown in  FIG. 2B , the non-polar liquid  12  is attached to the hydrophobic region  28  covering part of the hydrophilic surface  16 . As the hydrophobic region  28 , and, therefore, the attached non-polar liquid  12 , does not cover the entire hydrophilic surface  16 , some of the incident light  22  now emerges as emergent light  26 . 
     The bistable, electrowetting display picture element  30  transitions from the “Off” state to the “On” state through the application of a voltage between the transparent electrode  20  under the hydrophobic surface  18  and the polar liquid  14 . Application of such a voltage results in the well-known electrowetting effect in which the lower surface  18  becomes less hydrophobic, and more hydrophilic. This electrically induced change in the wetting properties of the lower surface  18  results in the non-polar liquid  12  beading up. If the applied voltage is above a predetermined threshold value, i.e., the voltage is of sufficient strength and duration, the non-polar liquid  12  beads up sufficiently to touch the hydrophobic region  28  covering the, upper hydrophilic surface  16 . Once the non-polar liquid  12  touches the upper, hydrophobic region  28 , it transitions there. Having transitioned to the upper hydrophobic region  28 , the non-polar liquid  12  spreads out to cover the entire upper, hydrophobic region  28 . The non-polar liquid  12  is, therefore, no longer in contact with the lower surface  18 . The non-polar liquid  12 , therefore, remains in an “On” state, attached to the upper hydrophobic region  28 , even when no further voltage is applied between the lower transparent electrode  20  and the polar liquid  14 . 
     The bistable, electrowetting display picture element  30  may be made to transition back from the “On” state shown in  FIG. 2B  to the “Off” state shown in  FIG. 2A  by the application of a suitable voltage between the upper, transparent electrode  20  under the hydrophobic region  28  and the polar liquid  14 . Application of such a voltage that is above a predetermined threshold, now results in the well-known electrowetting effect changing the wetting properties of the surface in region  28 . The surface in region  28  becomes less hydrophobic and more hydrophilic, resulting in the non-polar liquid  12  beading up. If the applied voltage is above a predetermined threshold, i.e. the voltage is of sufficient strength and duration, the non-polar liquid  12  beads up and touches the lower, hydrophobic surface  18 . Once the non-polar liquid  12  touches the lower, hydrophobic surface  18  it transitions to that surface and spreads out over it. Once spread out over the lower surface  18 , the non-polar liquid  12  no longer touches the upper region  28 . The non-polar liquid  12 , therefore, remains in the “Off” state, attached to the lower surface  18  even when no further voltage is applied between the upper transparent electrode  20  and the polar liquid  14 . 
       FIG. 3  is a schematic cross-sectional view of an exemplary reflection mode, bistable, picture element transitioning from an “Off” state  32  to an “On” state  34  and back again. 
     In the “Off” state  32 , the incident light  22  is partially or completely absorbed by the non-polar liquid  12  and any added dyes or pigments it may contain. 
     The reflection mode, bistable, picture element may be made to transition from the “Off” state  32  to the “On” state  34  by applying a suitable “On” switching voltage  36  between the polar liquid  14  and a lower, transparent electrode  38 . The “On” switching voltage  36  causes the wetting properties of the lower surface  18  to change from hydrophobic to more hydrophilic, and the non-polar liquid  12  to bead up. The threshold value of the suitable voltage  36  depends on the thickness of the hydrophobic surface  18 , the type and amount of non-polar liquid  12  and the distance between the lower, hydrophobic surface  18  and the upper hydrophobic region  28 . For a hydrophobic surface  18  having a thickness of approximately 1 μm, a non-polar liquid  12  that is an oil having a thickness of approximately 10 μm and a distance between the lower, hydrophobic surface  18  and the upper hydrophobic region  28  of about 100 μm, a suitable threshold voltage may, for instance, be in the range of 10 to 30 volts. That is, the application of a voltage that is greater than or equal to the threshold voltage to such a configuration will cause the non-polar liquid  12  that was covering the lower surface  18  to bead up sufficiently to touch the hydrophobic region  28 . The voltage  36  would need to be applied for a long enough time period for the non-polar liquid  12  to transition completely from one surface to the other, typically for a time in the range of 5 milliseconds to 50 milliseconds. 
     In one embodiment, the polar liquid  14  may be steered toward the hydrophobic region  28  by having a gap in the lower, transparent electrode  38  that corresponds to the location of the hydrophobic region  28 . In this way, the electric field set up by the applied voltage  36  will not change the wetting properties of the lower hydrophobic surface  18  in this vicinity as much as it does on the rest of the surface  18 . This results in the non-polar liquid  12  being steered toward this region, and, therefore, being positioned opposite the upper, hydrophobic region  28  as the non-polar liquid  12  beads up. 
     In an alternative embodiment, the lower, hydrophobic surface  18  may be made thicker in a region corresponding to the location of the upper, hydrophobic region  28 . As a result, the electric field set up by the applied voltage  36  will not change the wetting properties of the lower surface  18  in this vicinity as much it changes them on the rest of the surface  18 . This, too, results in the non-polar liquid  12  being steered toward this region, and, therefore, being positioned opposite the upper, hydrophobic region  28  as the non-polar liquid  12  beads up. 
     In the “On” state  34 , the non-polar liquid  12  remains confined to the hydrophobic region  28  even when the voltage  36  is no longer applied. Some of the incident light  22  is still absorbed by the non-polar liquid  12 , but a fraction of the incident light  22  reaches the lower reflecting support  42  and is reflected back to emerge as reflected light  40 . The ratio of reflected light  40  to incident light  22  is dependant, in part, on the ratio of the area of the upper, hydrophobic region  28  to the area of the entire picture element. 
     The reflection mode, bistable, picture element may be made to transition from the “On” state  34  to the “Off” state  32  by a suitable “Off” switching voltage  37  applied between the polar liquid  14  and an upper, transparent electrode  39 , thereby changing the wetting characteristics of the region  28  from hydrophobic to more hydrophilic. As a result of the change in wetting properties of region  28 , the non-polar liquid  12  that was attached to it will bead up. If the applied voltage is above an “Off” switching voltage threshold, the non-polar liquid  12  will bead up sufficiently to bridge the distance between the region  28  and the lower surface  18 . Once the non-polar liquid  12  touches the hydrophilic lower surface  18  it will transition there. The threshold value of the “Off” switching voltage  37  depends on the thickness of the hydrophobic surface  18 , the type and amount of non-polar liquid  12  and the distance between the upper, hydrophobic region  28  and the lower, hydrophobic surface  18 . The voltage  36  would need to be applied for a long enough time period for the non-polar liquid  12  to transition completely from one surface to the other, typically for a time in the range of 5 milliseconds to 50 milliseconds. 
       FIG. 4  is a schematic plan view of an exemplary bistable, electrowetting picture element transitioning from an “Off” state  32  to an “On” state  34  and back again. 
     In the “Off” state  32 , the non-polar liquid  12  is spread over the entire picture element surface  43 . In the “Off” state  32 , all incident light  22  may, therefore, be absorbed by the non-polar liquid  12  and any dyes or pigments it contains. Application of the suitable “On” switching voltage  36  between the polar liquid  14  and the lower, transparent electrode  38  results in the lower surface  18  becoming more hydrophilic and the non-polar liquid  12  beading up to occupy a small portion  46  of the picture element surface. When sufficiently beaded up, the non-polar liquid  12  touches the upper hydrophobic region  28  and transitions to that surface. The small portion  46  of the lower surface  18  occupied by the non-polar liquid  12  when it is beaded up sufficiently to reach the upper hydrophobic region  28  may be as little as 20% of the picture element area. 
     Once the non-polar liquid  12  transitions to the upper hydrophobic region  28 , it spreads out and occupies the entire upper hydrophobic region  28 , resulting in the stable “On” state  34  in which the non-polar liquid  12  only covers a portion  48  of the entire picture element. The portion  48  of the picture element covered by the non-polar liquid  12  in the “On” state  34  may be as little as 25% of the entire picture element. 
     Application of as suitable “Off” switching voltage  37  between the polar liquid  14  and the upper, transparent electrode  39  results in the upper region  28  becoming more hydrophilic and the non-polar liquid  12  beading up to occupy a smaller portion  50  of what was the upper hydrophobic region  28 . If the applied voltage is above a predetermined “Off” switching threshold voltage  37 , the non-polar liquid  12  will bead up sufficiently to touch the lower hydrophobic region  18 , and then transition to that surface. The smaller portion  50  of the upper region  28  may be as little as 20% of the picture element area when the non-polar liquid  12  is sufficiently beaded up to touch and make the transition to the lower hydrophobic region  18 . 
     Once the non-polar liquid  12  transitions to the lower hydrophobic region  18 , it spreads out and occupies the entire lower hydrophobic region  18 , resulting in the stable “Off” state  32  in which the non-polar liquid  12  covers the entire picture element. 
       FIG. 5  is a schematic cross-section of a further exemplary bistable, electrowetting picture element  30  of the present invention in an “Off” state. 
     The bistable, electrowetting display picture element  30  comprises a lower support plate  42  having a lower electrode  21  and a lower surface  18  that is hydrophobic. The area of a picture element is defined by a hydrophilic picture element defining barrier  52 . The bistable, electrowetting display picture element  30  further comprises an upper support plate  44  that is typically transparent. The upper support plate  44  has an upper, transparent electrode  19 , an upper surface  17  that is hydrophobic and a hydrophilic picture element defining barrier  52 . The upper surface  17  may be divided into sub-picture regions  56  by a hydrophilic, sub-picture region dividing wall  58 . An immiscible polar liquid  14  and non-polar liquid  12  are contained between the surface  18  of the lower support plate  42  and the surface  17  of the upper support plate  44 . 
     The bistable, electrowetting display picture element  30  also comprises a common electrode  54  that may, for instance, be a thin metal coating, or thin metal foil, located on top of the hydrophilic, sub-picture region dividing wall  58 , or sandwiched between the upper and lower hydrophilic picture element defining barrier  52 , or some combination thereof. 
     In a preferred embodiment, the upper support plate  44  is a transparent sheet such as, but not limited to, a transparent plastic or glass. The lower support plate  42  may be a similar transparent sheet if the bistable, electrowetting display picture element  30  is used in transmission mode, or it may be a reflective or diffusive material such as, but not limited to, a suitable plastic or reflective coated plastic, glass or metal, if the bistable, electrowetting display picture element  30  is used in reflective mode. The upper, transparent electrode  19  may, for instance, be a thin indium tin oxide (ITO) coating, or a thin aluminum doped zinc oxide coating (ZAO), as is well known in the art. Similar, in a transmission mode bistable, electrowetting display picture element  30 , the lower electrode  21  may also be a transparent electrode comprised of a thin indium tin oxide (ITO) coating, or a thin aluminum doped zinc oxide coating (ZAO). The common electrode  54  may also be such a transparent electrode. 
     The upper surface  17  and the lower surface  18  are both thin coatings that are both good dielectrics and hydrophobic. In a preferred embodiment, both the upper surface  17  and the lower surface  18  are comprised of an amorphous fluoropolymer such as, but not limited to, polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer resin (PFA) or fluorinated ethylene-propylene (FEP) all of which are sold by DuPont Inc. of Delaware under the tradename Teflon™. The thickness of the amorphous fluoropolymer is typically in the range of 0.5 to 2 μm. 
     The non-polar liquid  12  may be an oil such as, but not limited to, silicone oil or an alkane such as, but not limited to, hexadecane. The oil or alkane may be colored with suitable, well-known dyes or pigments including, but not limited to, suitable organic dyes in order to absorb, partially or fully, one or more spectral regions of light. 
     The polar liquid  14  is electroconductive and may, for instance, be water or a salt solution such as a solution of KCl in a mixture of water and ethyl alcohol. To operate in temperature ranges from −45 degrees C. to 200 degrees C., the polar liquid  14  may comprise a mixture that includes glycerol and alcohol. 
     The non-polar liquid  12  and the polar liquid  14  may also be selected to be matched in density so as to make the bistable, electrowetting display picture element  30  robust to motion or vibration. For instance, 1-brom-dodecane has the same density as a solution of a few percent of Na 2 SO 4  in water at room temperature. 
     In the “Off” state, the non-polar liquid  12  is in contact with the surface  18  that is hydrophobic. The non-polar liquid  12  is contained to the area of a picture element by a hydrophilic picture element defining barrier  52 . 
     By applying a suitable voltage between the lower electrode  21  and the common electrode  54 , the lower surface  18  may be made less hydrophobic, resulting in the non-polar liquid  12  beading up. With the right combination of amount of non-polar liquid  12 , thickness of lower surface  18 , separation of lower surface  18  from the upper surface  17  and a voltage above a predetermined threshold voltage value, the lower surface  18  may be made to bead up and touch upper surface  17 . As the upper surface  17  has no voltage applied across it, it remains hydrophobic. The lower surface  18  in contrast is now made more hydrophilic by the applied voltage that elicits the well-known electrowetting effect. Once the non-polar liquid  12  touches the upper surface  17  it, therefore, transfers to that surface. 
     In the bistable, electrowetting display picture element  30  of  FIG. 5  there is no need to steer the beading up non-polar liquid  12  in any particular direction, as each of the sub-picture regions  56  defined by the hydrophilic, sub-picture region dividing wall  58  are equal in area. Any beading up to the sufficient height will enable the non-polar liquid  12  to touch one of the sub-picture regions  56  and transition there. 
       FIG. 6  is a schematic cross-section of a further exemplary bistable, electrowetting picture element  30  of the present invention in an “On” state. The non-polar liquid  12  has transferred to the upper surface  17  and spread out, but is contained by the hydrophilic, sub-picture region dividing wall  58  to occupy a sub-picture region  56 . 
     For example, a 250 μm square picture element with an “Off” state non-polar liquid  12  thickness of 10 μm will bead up to a height of about 71 μm when it occupies 20% of the lower surface  18 . This degree of beading up has been shown to occur with an applied voltage above a threshold voltage of about 25 Volts for about 20 msecs when the lower surface  18  is a 0.8 μm thick amorphous fluoropolymer. With a surface to surface separation in the range of 60 μm to 70 μm, the non-polar liquid  12  may touch the upper surface  17  when such a voltage is applied. Once the non-polar liquid  12  is on the upper surface  17  it will spread out to fill the sub-picture region  56  defined by the hydrophilic, sub-picture region dividing wall  58 . If the sub-picture region  56  is 25% of the upper surface  17  area, the non-polar liquid  12  will now have a thickness of 40 μm and will allow 75% of any incident light  22  to be transmitted or reflected. The bistable, electrowetting display picture element  30  will remain in this “On” state indefinitely without any voltage being applied to either of the electrodes, and with no power being consumed. 
     By applying a suitable voltage between the upper, transparent electrode  19  and the common electrode  54 , the upper surface  17  may be made less hydrophobic, resulting in the non-polar liquid  12  beading up. With the right combination of amount of non-polar liquid  12 , thickness of upper surface  17 , separation of lower surface  18  from the upper surface  17  and a voltage above a predetermined threshold voltage value, the non-polar liquid  12  on the upper surface  17  may be made to bead up and touch the lower surface  18 . As the lower surface  18  has no voltage applied across it, it remains hydrophobic. The upper surface  17  in contrast is now made more hydrophilic by the applied voltage. Once the non-polar liquid  12  touches the lower surface  18  it, therefore, transfers to that surface, and spreads out to create a stable off-state, as shown in  FIG. 5 . 
       FIG. 7A  shows a hydrophilic picture element defining barrier  52  defining a single square picture element  60 . The hydrophilic picture element defining barrier  52  may, for instance, be a suitably etched polymer layer. 
       FIG. 7B  shows a square picture element, defined by a hydrophilic picture element defining barrier  52 , subdivided into four equal sub-picture regions  56  by a hydrophilic, sub-picture region dividing wall  58 . Each of the sub-picture regions  56  has an area that is approximately 25% of the area of the picture element  60 . The hydrophilic, sub-picture region dividing wall  58  may also be a suitably etched polymer layer and may be higher than, lower than, or the same height as the hydrophilic picture element defining barrier  52 . 
       FIG. 7C  shows a square picture element, defined by a hydrophilic picture element defining barrier  52 , subdivided into nine equal sub-picture regions  56  by a hydrophilic, sub-picture region dividing wall  58 . Each of the sub-picture regions  56  has an area that is approximately 11% of the area of the picture element  60 . 
       FIG. 7D  shows a square picture element, defined by a hydrophilic picture element defining barrier  52 , subdivided into five equal sub-picture regions  56  by a hydrophilic, sub-picture region dividing wall  58 . Each of the sub-picture regions  56  has an area that is approximately 20% of the area of the picture element  60  even though the sub-picture region  56  are not all congruent. 
       FIG. 8A  shows a schematic plan view of a picture element in an “On” state that has four sub-picture regions. The picture element  60  has three “On” sub-picture regions  57  and one “Off” sub-picture region  59 . The picture element  60  of  FIG. 8A  has a hydrophilic, sub-picture region dividing wall  58  as shown in  FIG. 7B . Such a hydrophilic, sub-picture region dividing wall  58  limits the non-polar, light absorbing, liquid  12  to the “Off” sub-picture region  59 . As a result, approximately 75% of any incident light  22  is either transmitted, or reflected, by the picture element  60 . 
       FIG. 8B  shows a schematic plan view of a picture element in an “On” state that has five sub-picture regions. The picture element  60  has four “On” sub-picture regions  57  and one “Off” sub-picture region  59 . The picture element  60  of  FIG. 8B  has a hydrophilic, sub-picture region dividing wall  58  as shown in  FIG. 7D . Such a hydrophilic, sub-picture region dividing wall  58  limits the non-polar, light absorbing, liquid  12  to the “Off” sub-picture region  59 . As a result, approximately 80% of any incident light  22  is either transmitted, or reflected, by the picture element  60 . 
       FIG. 8C  shows a schematic plan view of a picture element in an “On” state that has nine sub-picture regions. The picture element  60  has eight “On” sub-picture regions  57  and one “Off” sub-picture region  59 . The picture element  60  of  FIG. 8B  has a hydrophilic, sub-picture region dividing wall  58  as shown in  FIG. 7C . Such a hydrophilic, sub-picture region dividing wall  58  limits the non-polar, light absorbing, liquid  12  to the “Off” sub-picture region  59 . As a result, approximately 89% of any incident light  22  is either transmitted, or reflected, by the picture element  60 . 
       FIG. 9A  shows a plan view of an exemplary picture element  60  divided into three regions of unequal area. The smallest region  62  may, for instance have an area that is in a range of 5% to 20% of the total area of the picture element  60 . The mid-sized region  64  may, for instance have an area that is in a range of 15% to 40% of the total area of the picture element  60 . The large region  66  may, for instance have an area that is in a range of 40% to 80% of the total area of the picture element  60 . Such a picture element  60  is one way of achieving some degree of grey scale for the individual picture elements. 
       FIG. 9B  shows a plan view of an exemplary structure of the lower electrode  21  configured to drive the picture element of  FIG. 9A . The lower electrode  21  for each picture element is divided into five regions, A, B, C, D, and E that may be addressed individually or in combination. Three of the regions are essentially narrow wires with a small island region. Electrode region A has a first, small island region  68 . Electrode region C has a second, small island region  70 . Electrode region E has a third, small island region  72 . 
     When a voltage is applied to regions B, C, D and E, but not to A then the first, small island region  68  will be an area in which the electrowetting effect will be less than over the rest of the pixel. The non-polar liquid  12  will, therefore, be pushed toward the first, small island region  68  as it bead up, so that when sufficiently beaded up, the non-polar liquid  12  will touch the upper surface  17  within the smallest region  62  defined by the hydrophilic, sub-picture region dividing wall  58 . The result will, in this example, be an “On” state in which 80% to 95% of the light is either transmitted or reflected by the picture element. 
     When a voltage is applied to regions A, B, D and E, but not to C then the second, small island region  70  will be an area in which the electrowetting effect will be less than over the rest of the pixel. The non-polar liquid  12  will, therefore, be pushed toward the second, small island region  70  as it beads up, so that when sufficiently beaded up, the non-polar liquid  12  will touch the upper surface  17  within the mid-sized region  64  defined by the hydrophilic, sub-picture region dividing wall  58 . The result will, in this example, be an “On” state in which 60% to 85% of the light is either transmitted, or reflected, by the picture element. 
     When a voltage is applied to regions A, B, C and D, but not to E then the third, small island region  72  will be an area in which the electrowetting effect will be less than over the rest of the pixel. The non-polar liquid  12  will, therefore, be pushed toward the third, small island region  72  as it beads up, so that when sufficiently beaded up, the non-polar liquid  12  will touch the upper surface  17  within the large region  66  defined by the hydrophilic, sub-picture region dividing wall  58 . The result will, in this example, be an “On” state in which 20% to 60% of the light is either transmitted or reflected by the picture element. 
       FIG. 10  shows a schematic plan view of a multi-region structure  78 . The multi-region structure is a substrate  80  having a hydrophilic surface  82  in which there are a multiplicity of hydrophobic regions  84 . The hydrophobic regions  84  may, for instance, be picture elements having a hydrophobic surface that is, for instance, an amorphous fluoropolymer. 
       FIG. 11  shows a schematic cross-sectional view of the multi-region structure  78 . 
       FIG. 12  shows a schematic cross-sectional view of the multi-region structure loaded with non-polar liquid. Each of the hydrophobic regions  84  now has a droplet of non-polar liquid  86  loaded onto it. The non-polar liquid  86  may, for instance, be an oil, such as silicone oil. The non-polar liquid  86  droplets may all be of substantially the same volume and loaded by a technique such as dipping the multi-region structure  78  into a container of the non-polar liquid  86  and withdrawing the multi-region structure  78  at a controlled, even rate. 
       FIG. 13  shows a schematic cross-sectional view of an exemplary configuration for loading a multi-region structure with non-polar liquid. The non-polar liquid  86  is floating in a thin layer on top of a higher density liquid  88 . The higher density liquid  88 , that may for instance be water, is contained in a container  90 . The multi-region structure  78  is lowered into the container  90  through the layer of non-polar liquid  86  until all the hydrophobic regions  84  are submersed. The multi-region structure  78  is then withdrawn from the container  90  at a controlled, uniform rate. The result is that each of the hydrophobic regions  84  of the multi-region structure  78  is loaded with substantially the same amount of non-polar liquid  86 . Such a process may, for instance, be a useful method of loading a multi-picture element display substrate with uniform amounts of colored silicone oil as part of the process of manufacturing a display. 
       FIG. 14  shows a schematic cross-sectional view of a further exemplary configuration for loading a multi-region structure with non-polar liquid. 
     The multi-region structure  78  is lowered into the container  90  through the layer of non-polar liquid  86  floating on top of the higher density liquid  88 . The container  90  has a first valve  92  that connects the container  90  to a storage module  96 . The storage module  96  has a second valve  94  and a door  102 . The storage module  96  may also contain a rack  98  having locators  100 . 
     With first valve  92  and second valve  94  open, the multi-region structure  78  may, after being lowered through the layer of non-polar liquid  86 , be lowered onto rack  98  and be supported by one of the locators  100 . The rack  98  may then be moved horizontally, and another multi-region structure  78  lower through the layer of non-polar liquid  86  and into the next locator  100  on the rack  98 . 
     When rack  98  is fully loaded with multi-region structures  78 , each having all the hydrophobic regions  84  loaded with the same amount of non-polar liquid  86 , the first valve  92  and the second valve  94  may be closed. The storage module  96  may then be turned over so that door  102  may be opened without spilling the higher density liquid  88  contained in the storage module  96 . The rack  98  may then be removed so that the multi-region structures  78  may move on to the next stage in manufacturing a display. 
       FIG. 15  shows a schematic cross-sectional view of an exemplary configuration for loading a roll of multi-region structure with non-polar liquid. 
     A first reel  104  contains a flexible, multi-region material  106 . The flexible, multi-region material  106  may, for instance, be a polymer sheet having coatings to make it suitable for use as the support layer in an electrowetting picture display. Such coatings may, for instance, include a transparent electrode layer and a hydrophobic surface layer as well as a hydrophilic well structure for defining the extent of individual picture elements. The flexible, multi-region material  106  is feed from the first reel  104  through a layer of non-polar liquid  86  floating on a higher density liquid  88  contained in a container  116 . The layer of non-polar liquid  86  may be contained to a portion of the container  116  by a retaining wall  108 . 
     By feeding the flexible, multi-region material  106  through the layer of non-polar liquid  86  at a consistent, uniform rate, each of the hydrophobic regions  84 , that may each be picture elements, may be loaded with a uniform amount of non-polar liquid  86 . 
     The flexible, multi-region material  106  may then be fed by guiding rollers  110  onto a take up reel  114 . 
     There may also be an additional reel  112  that may, for instance contain a flexible material suitable for the top layer of an electrowetting display. The additional reel  112  may be used to complete the next step in manufacturing the display by adding the top layer of the display. In that way, the material collected on take up reel  114  may be a completed, flexible display having both a front and back support as well as being filled with the appropriate amounts of the non-polar liquid  86  and the higher density liquid  88 . 
     Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed invention. Modifications may readily be devised by those ordinarily skilled in the art without departing from the spirit or scope of the present invention.