Patent Publication Number: US-9423606-B2

Title: Method of manufacturing an electrowetting device

Description:
BACKGROUND 
     Known methods of manufacturing an electrowetting device can require large volumes of fluid for dispensing a relatively small amount of the fluid for the finally manufactured device. This can lead to inefficiencies in manufacture, for example wasting of unused volumes of fluid which can be expensive and high rates of evaporation of fluids being dispensed. 
     It is desirable to provide a more efficient method of fluid dispensing for manufacture of an electrowetting device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows schematically an example display element; 
         FIG. 2  shows a plan view of the example display element; 
         FIGS. 3 to 6  each show different examples of a part of a method of manufacturing an electrowetting device; and 
         FIGS. 7 and 8  show flow diagrams of examples of a method of manufacturing an electrowetting device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a diagrammatic cross-section of part of an example of an electrowetting display device  1 , including a plurality of picture elements or display elements  2 , one of which is shown in the Figure and which may also be referred to as an electrowetting cell. The lateral extent of the display element is indicated in the Figure by two dashed lines  3 ,  4 . The display elements comprise a first support plate  5  and a second support plate  6 . The support plates may be separate parts of each display element, but the support plates may be shared in common by the plurality of display elements. The support plates may include a glass or polymer substrate  6 ,  7  and may be rigid or flexible. In manufacturing examples described below the substrate is sufficiently flexible, transparent and may be formed for example of polycarbonate or polyethylene naphthalate (PEN), “polyester  12 , 13 ” or poly (ethylene terephthalate), or any other suitable material as the skilled person will appreciate. 
     The display device has a viewing side  8  on which an image or display formed by the display device can be viewed and a rear side  9 . In the Figure a surface of the first support plate  5 , which surface is in this example a surface of the substrate  7 , defines the rear side  9 ; a surface of the second support plate  6 , which surface is in this example a surface of the substrate  6 , defines the viewing side; alternatively, in other examples, a surface of the first support plate may define the viewing side. The display device may be of the reflective, transmissive or transflective type. The display device may be an active matrix driven display device. The plurality of display elements may be monochrome. For a color display device the display elements may be divided in groups, each group having a different color; alternatively, an individual display element may be able to show different colors. 
     A space  10  of each display element between the support plates is filled with two fluids: a first fluid  11  and a second fluid  12  at least one of which may be a liquid. The second fluid is immiscible with the first fluid. Therefore, the first fluid and the second fluid do not substantially mix with each other and in some examples do not mix with each other to any degree. The immiscibility of the first and second fluids is due to the properties of the first and second fluids, for example their chemical compositions; the first and second fluids tend to remain separated from each other, therefore tending not to mix together to form a homogeneous mixture of the first and second fluids. Due to this immiscibility, the first and second fluids meet each other at an interface which defines a boundary between the volume of the first fluid and the volume of the second fluid; this interface or boundary may be referred to as a meniscus and is shown in  FIG. 1  as an interface  57  with first fluid contracted with a voltage applied and as an interface  55  when a zero voltage is applied. With the first and second fluids substantially not mixing with each other, it is envisaged in some examples that there may be some degree of mixing of the first and second fluids, but that this is considered negligible in that the majority of the volume of first fluid is not mixed with the majority of the volume of the second fluid. 
     The second fluid is electrically conductive or polar and may be water, or a salt solution such as a solution of potassium chloride in water. The second fluid may be transparent; it may instead be colored or absorbing. The first fluid is electrically non-conductive and may for instance be an alkane like hexadecane or may be an oil such as silicone oil. 
     The first fluid may absorb at least a part of the optical spectrum. The first fluid may be transmissive for a part of the optical spectrum, forming a color filter. For this purpose the first fluid may be colored by addition of pigment particles or a dye. Alternatively, the first fluid may be black, i.e. absorb substantially all parts of the optical spectrum, or reflecting. A reflective first fluid may reflect the entire visible spectrum, making the layer appear white, or part of it, making it have a color. In examples to be described below, the first fluid is black and therefore absorbs substantially all parts of the optical spectrum, for example in the visible light spectrum. The term “substantially absorbs” includes a degree of variation, therefore the first fluid may not absorb all wavelengths, but the majority of wavelengths within a given spectrum such as the visible spectrum, so as to perform the function of the first fluid in the element. The first fluid is therefore configured to absorb substantially all light incident on the first fluid. For example the first fluid may absorb 90% or more of light in the visible spectrum and incident on the first fluid. The support plate  5  includes an insulating layer  13 . The insulating layer may be transparent or reflective. The insulating layer  13  may extend between walls of a display element. To avoid short circuits between the second fluid  12  and electrodes arranged under the insulating layer, layers of the insulating layer may extend uninterrupted over a plurality of display elements  2 , as shown in the Figure. The insulating layer has a surface  14  facing the space  10  of the display element  2 . In this example the surface  14  is hydrophobic. The thickness of the insulating layer may be less than 2 micrometers and may be less than 1 micrometer. 
     The insulating layer may be a hydrophobic layer; alternatively, it may include a hydrophobic layer  15  and a barrier layer  16  with predetermined dielectric properties, the hydrophobic layer  15  facing the space  10 , as shown in the Figure. The hydrophobic layer is schematically illustrated in  FIG. 1  and may be formed of Teflon® AF1600. The barrier layer  16  may have a thickness, taken in a direction perpendicular the plane of the substrate, between 50 nanometers and 500 nanometers and may be made of an inorganic material like silicon oxide or silicon nitride or a stack of these (for example, silicon oxide—silicon nitride—silicon oxide) or an organic material like polyimide or parylene. 
     The hydrophobic character of the surface  14  causes the first fluid  11  to adhere preferentially to the insulating layer  13 , since the first fluid has a higher wettability with respect to the surface of the insulating layer  13  than the second fluid  12 . Wettability relates to the relative affinity of a fluid for the surface of a solid. Wettability may be measured by the contact angle between the fluid and the surface of the solid. The contact angle is determined by the difference in surface tension between the fluid and the solid at the fluid-solid boundary. For example, a high difference in surface tension can indicate hydrophobic properties. 
     Each display element  2  includes a first electrode  17  as part of the support plate  5 . In examples shown there is one such electrode  17  per element. The electrode  17  is electrically insulated from the first and second fluids by the insulating layer  13 ; electrodes of neighboring display elements are separated by a non-conducting layer. In some examples, further layers may be arranged between the insulating layer  13  and the electrode  17 . The electrode  17  can be of any desired shape or form. The electrode  17  of a display element is supplied with voltage signals by a signal line  18 , schematically indicated in the Figure. 
     The support plate  6  includes a second electrode  19 , which may extend between walls of a display element or extend uninterruptedly over a plurality of display elements  2 , as shown in the Figure. The electrode  19  is in electrical contact with the conductive second fluid  12  and is common to all display elements. The electrode may be made of for example the transparent conductive material indium tin oxide (ITO). A second signal line  20  is connected to the electrode  19 . Alternatively, the electrode may be arranged at a border of the support plates, where it is in electrical contact with the second fluid. This electrode may be common to all elements, when they are fluidly interconnected by and share the second fluid, uninterrupted by walls. The display element  2  can be controlled by a voltage V applied between the signal lines  18  and  20 . The signal line  18  can be coupled to a matrix of control lines on the substrate  7 . The signal line  20  is coupled to a display driving system. 
     The first fluid  11  in this example is confined to one display element by walls  21  that follow the cross-section of the display element. The cross-section of a display element may have any shape; when the display elements are arranged in a matrix form, the cross-section is usually square or rectangular. Although the walls are shown as structures protruding from the insulating layer  13 , they may instead be a surface layer of the support plate that repels the first fluid, such as a hydrophilic or less hydrophobic layer. The walls may extend from the first to the second support plate but may instead extend partly from the first support plate to the second support plate as shown in  FIG. 1 . The extent of the display element, indicated by the dashed lines  3  and  4 , is defined by the center of the walls  21 . The area of the surface  14  between the walls of a display element, indicated by the dashed lines  22  and  23 , is called the display area  24 , over which a display effect occurs. The display effect depends on an extent that the first and second fluids adjoin the surface defined by the display area, in dependence on the magnitude of the applied voltage V described above. The magnitude of the applied voltage V therefore determines the configuration of the first and second fluids within the electrowetting element. In other words, the display effect depends on the configuration of the first and second fluid in the display element, which configuration depends on the magnitude of the voltage applied to the electrodes of the display element. The display effect gives rise to a display state of the display element for an observer looking at the display device. When switching the electrowetting element from one fluid configuration to a different fluid configuration the extent of second fluid adjoining the display area surface may increase or decrease, with the extent of first fluid adjoining the display area surface decreasing or increasing, respectively. 
       FIG. 2  shows a matrix of rectangular picture elements in a plan view of the hydrophobic surface  14  of the first support plate. The extent of the central picture element in  FIG. 2 , corresponding to the dashed lines  3  and  4  in  FIG. 1 , is indicated by the dashed line  26 . Line  27  indicates the inner border of a wall; the line is also the edge of the display area  23 . 
     When a zero or substantially zero voltage is applied between the electrodes  17  and  19 , i.e. when the electrowetting element is in an off state, the first fluid  11  forms a layer between the walls  21 , as shown in the  FIG. 1 . Application of a voltage will contract the first fluid, for example against a wall as shown by the dashed shape  25  in  FIG. 1  or  FIG. 2 . The controllable shape of the first fluid, in dependence on the magnitude of applied voltage, is used to operate the picture element as a light valve, providing a display effect over the display area  23 . For example, switching the fluids to increase adjoinment of the second fluid with the display area may increase the brightness of the display effect provided by the element. 
     This display effect determines the display state an observer will see when looking towards the viewing side of the display device. The display state can be from black to white with any intermediate grey state; in a color display device, the display state may also include color. 
       FIG. 3  shows schematically part of an example method of manufacturing an electrowetting display device. For clarity of description, apparatus used in the manufacturing process is described in conjunction with the method provided by the apparatus for manufacturing the device. However it is to be appreciated that this description includes a description of the apparatus separately, i.e. when not in use and without the presence of the materials and components of the display device being assembled to manufacture the device.  FIG. 7  is a flow diagram showing parts of an example manufacturing process described herein. 
     Apparatus for providing a method of manufacturing an electrowetting device according to examples described herein includes a first support plate feeding system configured to provide a first support plate and a second support plate feeding system configured to provide a second support plate. 
     In the examples to be described, the first support plate and the second support plate for manufacturing a display device are each provided separately from each other and are at least partially pre-assembled. So, in examples described herein, the support plate fed by the first support plate feeding system may be the first support plate as described above with reference to  FIG. 1  and the support plate fed by the second support plate feeding system may be the second support plate as described above with reference to  FIG. 2 . For clarity of illustration, in  FIGS. 3 to 6  the first and second support plates are each shown schematically as a single layer, without showing separate layers forming the plates. For example, the walls of the first support plate are not illustrated, though it is to be appreciated that they are present when the first support plate is being fed through apparatus described below. 
     For some examples of manufacture described herein, the method may be referred to as a “roll to roll” technique involving feeding of the first and second support plates through the manufacturing process using a series of rollers. Accordingly, each of the first and second support plates to be fed through the manufacturing apparatus needs to be sufficiently flexible to be manipulated by the rollers without causing the plates damage. Thus, as explained above, the substrate in such examples is sufficiently flexible to bend around at least part of a roller, for being fed during the roll to roll technique. Such flexibility applies also to other parts of the first and second support plates, including the insulating layer, the barrier layer, the wall material and the electrode described previously, such that the first and second support plates are sufficiently flexible to co-operate with the rollers in the roll to roll technique. The flexibility of the support plate is however limited where appropriate such that a manufactured electrowetting display device is sufficiently rigid for its intended purpose; therefore in some examples the support plates may be substantially rigid but with sufficient flexibility for their use in the roll to roll technique when exposed to mechanical forces used during the roll to roll technique; in other examples, where the display device is intended to be flexible, the first and second support plates may be less rigid. In examples, the materials from which the first and second support plates are made are chemically and mechanically compatible with the rollers such that there is no slip between each of the first and second support plates and respective rollers. Each of the first and second support plates may be fed respectively from a source, for example a roll of the first support plate and a roll of the second support plate, or in other examples each of the first and second support plates may be fed from an earlier stage of the manufacturing process where the first and second support plates were at least partly manufactured. Feeding of the first and second support plates is shown in  FIG. 3  by arrows F 1 , F 2  respectively. 
     The first and second support plates fed by the first and second feeding systems, respectively, may each be part of a larger sheet of a plurality of first support plates and second support plates, respectively. In other words, a sheet, otherwise referred to as a foil, fed by the first support plate feeding system, may be dividable into a plurality of first support plates after assembly of the display device, for example using a “scribe and break” process known to the skilled person. This may be done similarly for the second support plate. Using such a foil gives a more efficient manufacturing process so that numerous display devices may be assembled continuously and efficiently. 
     In this example the first support plate feeding system includes a first roller  30  and the second support plate feeding system includes a second roller  32  although in other examples different elements may be used instead of either of the first and second rollers, for example elements with an at least partly curved surface, to position the first and second support plates relative to each other for the manufacture process to be described. 
     The first support plate is wrapped at least partly around the first roller, passing from a first support plate source. The second support plate is wrapped at least partly around the second roller, after passing from a second support plate source. More specifically in this example an outer surface of each of the first and second support plates is wrapped at least partly around the respective first and second rollers. The first roller and the second roller are separated from each other and positioned relatively to each other such that the first support plate and second support plate are angled relatively to each other, i.e. the second support plate is angled relative to the first support plate and vice versa, to define, i.e. form, a cavity  34  between the first and second support plates. The cavity  34  narrows towards a constriction C between the first and second support plates. In this example the constriction is formed at a region between the first and second rollers  30 ,  32  where the first and second rollers are closest to each other, i.e. a narrowest region of the cavity between the rollers, which may be otherwise referred to as a nip between the rollers. The constriction in this example is shown in  FIG. 3  between the arrows labelled C 1  and C 2 . In this example the cavity  34  is substantially V-shaped; in other words the cavity between the first and second support plates tapers or narrows towards the constriction. A wider part of the cavity  34  above the constriction is formed between parts of the first and second rollers which are less close together than at the constriction. Substantially V-shaped includes shapes of the cavity  34  which have substantially flat sides, i.e. in some examples where flexible first and second support plates are pulled taut whilst being fed between rollers and in other examples despite there being non-flat walls on the first support plate and in other examples which do not have flat sides, for example where sides of the cavity  34  are curved due to a curved surface of each of the first and second rollers. For example, a first angle of the first support plate relative to the second support plate may be greater at a first position with a first distance between the first and second support plates than a second angle of the first support plate relative to the second support plate at a second position, at the constriction, between the first and second support plates. The first position corresponds with a wider part of the cavity and the second position corresponds with a narrower part of the cavity. With the first angle being greater than the second angle, the first and second support plates are in examples less parallel relative to each other at the first position compared with at the second position. Indeed, at the second position, at the constriction, parts of the first and second support plates may be substantially parallel to each other, i.e. parallel within acceptable manufacturing tolerances. 
     For manufacturing the display device, the cavity  34  is at least partly filled with the second fluid  12  (the second fluid  12  being shown in  FIG. 3  with shading). The second fluid may be provided in the cavity by a suitable second fluid supply system. The cavity  34  therefore functions as a reservoir of the second fluid for dispensing the second fluid between the first and second support plates. In other words, the cavity  34  functions as a container or funnel for the second fluid, with sides of the container or funnel being formed by the first support plate and the second support plate, from which container or funnel the second fluid may flow. This avoids the need to submerge support plates in a bath of the second fluid, as is done in known methods, to dispense the second fluid between the first and second support plates. Such known methods require considerably more second fluid than is needed to be dispensed between the first and second support plates, which can lead to inefficiencies in the manufacturing process, for example by requiring large volumes of possibly expensive fluids and leading to wasting or contamination of undispensed fluid and loss due to evaporation. In the new method of manufacture described in examples herein, using the first and second support plates to form the second fluid reservoir, so that there is no need to provide the second fluid on both sides of the first and/or second support plate for dispensing the second fluid between the first and second support plates, gives a more efficient method by for example reducing at least one of the inefficiencies described above. 
     It is noted that a volume of second fluid in the cavity need not be enclosed on all sides to be suitably contained to form the reservoir. In fact, in examples it is sufficient to use the first and second support plates to form the cavity; no barriers for example are required which lie in a plane parallel to the plane that  FIG. 3  is drawn in. Despite this, in such examples, the second fluid is contained within the cavity due to surface tension forces of the second fluid, provided that a distance between the first and second support plates in forming the cavity does not exceed a distance at which the surface tension forces are overcome, which would cause the second fluid to spill out of the cavity. Thus, in examples, the distance between the first and second support plates may be within a capillary length property of the second fluid when interfacing with a gas surrounding an exterior of the first and second support plates. As will be explained later, the first fluid may be dispensed using a channel. In examples, due to the surface tension forces of the second fluid which keep the second fluid within the cavity, the second fluid may also form a barrier of second fluid around the volume of first fluid in the channel, thereby preventing first fluid from spilling out of the cavity. 
     In examples the constriction may be provided at the lowest region of the cavity  34  to assist dispensing of the second fluid between the first and second support plates using gravity. Indeed, in such examples, the weight of the second fluid above the constriction can help apply pressure at the constriction to dispense and assist flow of the second fluid through the constriction. 
     To manufacture the display device the first support plate is fed and therefore moved over the first roller, in this example assisted by rotating the first roller in a first rotational direction R 1 , which in this example is clockwise, whilst moving the first support plate over the first roller. The second support plate is fed and therefore moved over the second roller, in this example assisted by rotating the second roller in a second rotational direction R 2 , which in this example is opposite the first rotational direction and is therefore anti-clockwise, whilst moving the second support plate over the second roller. 
     Given the positioning of the first and second rollers, moving the first support plate over the first roller and moving the second support plate over the second roller, in this example by rotating the rollers in the directions described, moves the first and second support plates towards the constriction and towards each other. In other words the first and second support plates are brought towards each other at the constriction. It is to be understood that in other examples the first support plate may be considered to be moved towards the second support plate whilst moving the first and second support plates towards the constriction, or vice versa. 
     At the constriction the first and second support plates are brought together with, in this example, a distance Dl between the two support plates which is substantially equal to a distance between the first and second support plates of the manufactured display device, thus setting the distance between the plates. Thus, after having been fed through the constriction, the distance between the first and second support plates is also substantially equal to the distance between the first and second support plates of the manufactured display device. The phrase “substantially equal” covers variations from the distance of the manufactured display device due to for example variations within acceptable manufacturing tolerances or a contraction of a sealing material (described later) due to curing. The distance Dl in this example is taken in a direction perpendicular to a surface of the second support plate adjoined by the second fluid. 
     Thus, at the constriction, the second fluid is dispensed between the first and second support plates, from the reservoir of second fluid in the cavity  34 , as a consequence of moving the first and second support plates towards the constriction, which brings the first and second support plates closer together, i.e. towards each other. Thus, during dispensing the first and second support plates are moved through the constriction and the second fluid is dispensed from the reservoir, through the constriction, to in-between the first and second support plates. As the second fluid is dispensed, it may in some examples be necessary to supply more of the second fluid into the cavity  34 , using a suitable second fluid supply system, to maintain a supply of second fluid for dispensing at the constriction whilst continuing to feed the first and second support plates. Further, supplying more of the second fluid may be necessary to maintain a channel of the first fluid described below. In other examples, the volume of the second fluid provided in the cavity may be sufficient for dispensing the second fluid for an intended duration of dispensing the second fluid. Dispensing of the second fluid may in examples be controlled in dependence on a rate of rotating the first and second rollers; therefore an appropriate rate may be chosen to ensure a satisfactory and stable flow of the second fluid. 
     The first fluid is dispensed on at least one part of a surface of the first support plate. In this example, the first fluid is dispensed on the surface of the display area of each display element of the first support plate. This is illustrated in  FIG. 3  as regions of the first fluid  11 . It is to be appreciated that the first fluid is dispensed on the surface of further display areas of the first support plate not illustrated; these include display areas of further of the sheet to be fed to the constriction but also further display areas across an extent of the first support plate taken in a plane perpendicular to the plane of the  FIG. 1 t    is to be noted that although the walls of display elements are not illustrated in  FIG. 3 , for clarity, they are indicated in  FIG. 3  with the label  21  where there is an interruption between regions of first fluid  11 . 
     To dispense the first fluid, the first fluid is provided in part of the cavity  34  between the first and second support plates using for example a first fluid supply system. More specifically, the first fluid is provided at least partly, in this example entirely, within a channel  36  formed between a part  38  of a surface of the first support plate and the second fluid  12 . The channel may have the form of a longitudinal depression in the second fluid, a groove, a trough or a longitudinal recess. The channel of first fluid is formed due to the immiscibility of the first and second fluids and therefore an interface, i.e. meniscus, between the first and second fluids defines, i.e. determines, a form of the channel. A sufficient volume of first fluid is supplied adjacent to the first support plate, on a surface of the second fluid in the cavity  34 , to form the channel of first fluid. Therefore, the channel of first fluid functions as a reservoir of first fluid for dispensing the first fluid on the surface of the first support plate. Given the hydrophobic properties of the display areas of the first support plate, the first fluid rather than the second fluid tends to wet the display areas. Thus, as the first support plate is moved towards the constriction, in this example by moving the first support plate over the first roller, the part  38  of the surface of the first support plate is moved along a side of the channel  38  and the display areas are wet by the first fluid. As the first support plate continues to be moved towards the constriction, the display areas remain coated with the first fluid, these being dispensed regions of first fluid for the manufactured display device.  FIG. 3  shows a region of first fluid being formed as an extruded region of first fluid extending along the surface of the first support plate from the channel  38 . As the walls are less hydrophobic than the display areas and are therefore less wettable to the first fluid than to the second fluid, being for example hydrophilic, the walls are not coated with the first fluid given the preference of the first fluid to wet the display areas. Dispensing of the first fluid, for example the thickness of the first fluid layer formed on each display area, may be controlled by controlling one or more of the following: the angle of the first support plate, a speed of moving the part  38  of the surface of the first support plate along the side of the channel, in this example the speed of feeding the first support plate over the first roller; the volume of first fluid in the channel; the volume of the second fluid in the cavity; or the properties of the first fluid such as the wettability of the first fluid for the display areas. In some examples it may be necessary to supply more of the first fluid in the channel during dispensing of the first fluid on the surface of the first support plate, using a first fluid supply system, to maintain a supply of the first fluid in the channel; in other examples the volume of first fluid in the channel may be sufficient for the intended duration of dispensing the first fluid. In examples, as the skilled person will understand, the shape of the channel may be controlled using one or more of: controlling a shape of the channel using one or more of: a position of the further surface relative to the part of the surface of the first support plate; a spacing between the further surface and the part of the surface of the first support plate, a wettability of the further surface for the first fluid, a wettability of the further surface for the second fluid, a volume of the provided second fluid, a volume of the provided first fluid, a surface tension property of the first fluid, a surface tension property of the second fluid, an extent of immiscibility of the first and second fluids, a density of the first fluid, a density of the second fluid, a shape of the interface between the first and second fluids, a shape of the further surface, or an angle of the part of the surface of the first support plate relative to the further surface. 
     In examples a sealing material for coupling the first support plate with the second support plate is dispensed on a surface of a part of the second support plate before that part of the second support plate reaches the constriction during moving the first and second support plates towards the constriction. Although for clarity the sealing material is not shown in  FIG. 3 , a sealing material dispensing system  40  for dispensing the sealing material is illustrated. The sealing material in examples is for forming a sealing element for sealing a perimeter of a display device and which therefore may be formed as a rectangular or square shaped seal for example for surrounding a matrix of display elements of the display device being manufactured. Therefore, the sealing material may be dispensed with a suitable shape and of sufficient thickness for coupling the first and second support plates at the constriction. The sealing material is dispensed in this example before the constriction and feeding the second support plate moves the sealing material towards the constriction C. At the constriction C where the first and second support plates are closest together, the first support plate is coupled with the second support plate by bringing the first support plate into contact with the sealing material dispensed on the part of the surface of the second support plate. The dispensing of the sealing material may be timed in coordination with the speed of rotating the first and second rollers and in dependence on a layout of display areas of the first support plate, including for example a sealing region (not illustrated) of the first support plate which lacks display areas and which surrounds a matrix of display areas for the display device, so that the first support plate is coupled with the second support plate at the desired location, i.e. the sealing region. The sealing material may be dispensed as a curable and mouldable compound such that, when dispensed with a thickness greater than the distance Dl, the constriction applies pressure to the sealing material via the first and second support plates, thereby compressing the sealing material between the first and second support plates to ensure suitable adhesion of the sealing material to each of the first and second support plates, to provide a suitable seal for the display device. With the sealing material being curable, the sealing material may be irradiated (not illustrated) with ultraviolet light after the constriction to cure the sealing material and thereby form the sealing element. In other examples the sealing material may be a pressure sensitive adhesive. 
     After the sealing material has been cured to form the sealing element and with the support plates having been fed through the constriction, the assembled display device is fed in the direction F 3  to be processed further, for example to divide the coupled first and second support plate sheets to form individual display devices. 
       FIG. 4  illustrates a different example of part of a method of manufacturing an electrowetting display device. Features of the apparatus and their role in manufacturing the display device are similar to those described using  FIG. 3  and are labelled in  FIG. 4  using the same reference numbers; corresponding descriptions apply. Differences in the example of  FIG. 4  compared with that of  FIG. 3  will therefore be described. 
     In this example of  FIG. 4  a dispensing of the first fluid on the display areas of the first support plate is performed differently than in  FIG. 3 . A further surface is provided in this example by a further element which in this example is a third roller  42  positioned relative to and spaced from the first support plate  5  to form a second constriction  44  in this example between the arrows labelled C 3  and C 4 . The second constriction is formed between the first support plate and a surface of the third roller  42  before a first support plate is fed to the constriction C. A tension in the first support plate, between the first roller  30  and not illustrated parts of the first support plate feeding system located before the first roller, maintain a position of a part of the first support plate relative to the surface of the third roller  42 , thereby defining, i.e. forming, the second constriction where the third roller is closest to a surface of the first support plate. The third roller  42  is positioned to be at least partly immersed in the second fluid in the cavity  34  between the first and second support plates. First fluid is supplied in a cavity  46  between part of the first support plate and the third roller. A channel  48  is formed between a part of the surface of the first support plate, the second fluid  12  in the cavity  34  between the first and second support plates and the surface of the third roller. As for the channel described previously, the channel  48  is formed due to the immiscibility of the first and second fluids and therefore an interface, i.e. meniscus, between the first and second fluids defines, i.e. determines, a form of the channel  48 . The form of the channel is influenced too by the position of the surface of the third roller  42  and therefore by the second constriction  44 . The first fluid is dispensed on the display areas of the first support plate by, and therefore at, the second constriction  44 , as the first support plate is moved towards the constriction C by the first roller  30 . More specifically, the part of the surface of the first support plate forming the channel  48  is moved along a side of the channel  48 . The second constriction  44 , specifically a size of a spacing between the further surface and the part of the surface of the first support plate, controls a thickness of the first fluid for dispensing the first fluid, the thickness in this example being taken in a direction perpendicular to the surface of the part of the first support plate at the second constriction  48 . For example, the second constriction  44  reduces a thickness of the first fluid and aids spreading of the first fluid across a surface of the first support plate for being coated by the first fluid. Factors described above for controlling dispensing the first fluid with reference to  FIG. 3  apply appropriately in this example too. 
     In this example, first fluid  50  is supplied on the surface  52  of the third roller  42  using a fourth roller  54 . The fourth roller is positioned relative to the third roller to provide a third constriction  56  between the third and fourth rollers, the third constriction being indicated by the arrows C 5  and C 6 . First fluid is provided at the third constriction  56 , for example by a first fluid supply system. The third constriction controls an amount of first fluid supplied on the surface of the third roller to form a layer and therefore an amount of first fluid provided by the third roller in the channel  48  between the third roller and the first support plate. The third roller is rotated in this example in an anticlockwise rotational direction R 3  to provide first fluid in the channel  48 , with in this example the fourth roller being rotated in an opposite rotational direction R 4 , i.e. clockwise in this example, to control providing of first fluid on the third roller, i.e. transferring of first fluid from the fourth roller to the third roller surface. The third roller may be rotated during the moving the part of the surface of the first support plate along the side of the channel. A speed of rotating the third roller, relative to the speed of the moving the part of the surface of the first support plate along the side of the channel, in examples controls a rate of dispensing the first fluid on the part of the surface of the first support plate. 
     In this example of  FIG. 4  the second roller  32  performs the function of the second roller described using  FIG. 3  but has a larger diameter than the first roller in this example, to form a deeper cavity  34 . Thus the cavity  34 , when filled with second fluid  12 , immerses part of the third roller, for forming the channel  48 . 
     Although walls of the first support plate are not illustrated, it is to be appreciated that the second constriction  44  is sized such that the walls of the first support plate may be fed through the second constriction  44  without damage. The third roller may therefore be positioned so as not to contact the walls as the first support plate is fed through the second constriction  44 . Further, in examples, the walls may have poor wettability for the first fluid, meaning that first fluid from the channel  48  may not be deposited on the walls; any first fluid which might be applied to the walls is skimmed off the walls by the first fluid in the channel of first fluid, thus further aiding accurate dispensing of the first fluid on the display areas. 
       FIG. 5  illustrates schematically another example of part of a manufacturing method of an electrowetting display device. Features of the apparatus and their role in manufacturing the display device are similar to those described using  FIG. 3  and are labelled in  FIG. 5  using the same references numbers; corresponding descriptions apply. Differences in the example of  FIG. 5  compared with that of  FIG. 3  will therefore be described. 
     In this example of  FIG. 5 , further features are described which are different compared with the example of  FIG. 3  but which have similarities to those described previously. Such features are labelled with the suffix “a” and take a similar description as given previously, but with differences now described. 
     In this example the second support plate  58  has a different construction than described previously and instead has in this example a similar construction to that of the first support plate. A further first fluid is provided in a further part of the cavity and within a further channel  36   a  formed between a part  60  of a surface of the second support plate and the second fluid  12 . The further first fluid may have the same composition as the first fluid  11  described previously or may be different, for example coloured with a different dye than the first fluid dispensed on the surface of the first support plate using the channel  36 . The further first fluid is dispensed on the part  60  of the surface of the second support plate by moving the second support plate towards the constriction C, as described previously, which moves the part  60  of the surface of the second support plate along a side of the further channel  60 , for dispensing the further first fluid as regions  11   a  of the further first fluid on display areas of the second support plate. 
     In the example of  FIG. 5  a further support plate  62  is provided, for example from a further support plate feeding system, as shown by arrow F 4 . The further support plate feeding system is configured to provide the further support plate angled relative to the second support plate to define, i.e. form, a further cavity  64  between the second support plate  58  and the further support plate  62 . In this example the further support plate has a similar construction as the first support plate  5 . The further cavity is formed between a surface of the second support plate  58  furthest away from the display area of the second support plate. The further cavity  64  narrows towards a further constriction  66 , indicated between arrows C 7  and C 8 , formed between the second support plate and the further support plate provided on a further roller  68  of the further support plate feeding system which roller is positioned for forming the further constriction. The further cavity  64  is at least partly filled with a further second fluid  12   a  which may be the same chemical composition as the second fluid  12  described previously or of a different composition. The further second fluid in the further cavity  64  therefore provides a further reservoir of the further second fluid for dispensing the further second fluid between the second support plate and the further support plate. 
     In this example the further support plate  62  is moved over a further element, in this example the further roller  68  which the further support plate is at least partly wrapped around. The further roller  68  functions in a similar way as the first roller, by moving the further support plate towards the further constriction  66  and towards the second support plate for dispensing the further second fluid at the second constriction, assisted by rotating R 5  the further roller. In other examples, the second support plate may be moved towards the further support plate or both the second and further support plates may be moved towards each other. 
     A further first fluid  72 , which may be the same or of a different composition than the first fluid described previously, is provided in part of the further cavity  64  and within a further channel  70 . The further channel  70  is formed between a part of the surface of the further support plate and the further second fluid, although in other examples the further channel may be formed between the second fluid and a part of the surface of the second support plate. The further channel functions in a similar manner as the channel  36  described using  FIG. 3  and that description should be taken to apply here, for dispensing the further first fluid by moving the appropriate one of the second support plate and the further support plate along a side of the further channel, to provide regions of the further first fluid  72  on display areas of the further support plate. A further first fluid supply system may be used for supplying the further first fluid in part of the further cavity to form and maintain the further channel of the further first fluid. A reservoir of the further second fluid in part of the further cavity may be formed and maintained using a further second fluid supply system (not illustrated) for supplying further second fluid into the further cavity. Further rollers may be used to assist supplying of the further first fluid as described similarly for supply of the first fluid using  FIG. 4 . 
     The second support plate and the further support plate are coupled together in this example in a similar way as coupling the first and second support plates described previously, using a further sealing material dispensing system  40   a  for dispensing a further sealing material on a surface of a part of the further support plate before reaching the further constriction during moving the second and further support plates towards the constriction, with the second and further support plates being coupled together by bringing the second and further support plates together, so the second support plate contacts the further sealing material; the previous description should be taken to apply here, modified accordingly. 
       FIG. 6  illustrates schematically a different example of part of a manufacturing method of an electrowetting display device. Features of the apparatus and their role in manufacturing the display device are similar to those described using  FIG. 3  and are labelled in  FIG. 6  using the same reference numbers; corresponding descriptions apply. Differences in the example of  FIG. 6  compared with that of  FIG. 3  will therefore be described. 
     In this example, a first support plate  74  is fed F 1  to and over the first roller  30 , by wrapping the first support plate at least partly around the first roller. In this example the first support plate has a construction similar to the second support plate described using  FIG. 3 . A further support plate  76 , also similar in construction to the second support plate of  FIG. 3 , is fed F 4  from an appropriate feeding system. In this example the further support plate is fed to and over the second roller  32 , by for example wrapping the further support plate at least partly around the second roller. A second support plate  78 , which in this example is similar in construction to the first support plate  5  described using  FIG. 3  but in this example may be comprised of a single substrate  7  with a stack of the electrode, barrier layer, hydrophobic layer and walls formed on two opposite and parallel surfaces of the substrate  7 . The second support plate is fed F 2  between the first and the further support plates  74 ,  76  using an appropriate feeding system. The first and second rollers  30 ,  32  are positioned separate from and relative to each other to form a constriction between the first and second rollers as indicated by arrows C 1  and C 2 . However, in this example, in contrast with that of  FIG. 3 , the constriction includes two constrictions; a constriction  80  between the first and second support plates and a constriction  82 , which may be referred to as a further constriction, between the second and further support plates. 
     The first support plate is angled relative to the second support plate and the further support plate is angled relative to the second support plate, to provide, respectively, a cavity  84  between the first support plate and the second support plate and a cavity  86  between the second support plate and the further support plate. These cavities are at least partly filled with a second fluid, which may be the same or different for each cavity  84 .  86 . In a similar manner as described previously, rotating the first and second rollers moves the first and further support plates over the first and second rollers respectively; also in this example by feeding the second support plate  78  appropriately, second fluid is dispensed by the constrictions  80 ,  82 , respectively between the first and second support plates and between the second and further support plates, by moving at least one of the first and second support plates and at least one of the second and further support plates towards each other, to bring them together. 
     A channel  88 ,  90  of a first fluid is formed in each of the cavities  84 ,  86 . The channels  88 ,  90  are each similar to the channel described previously using  FIG. 3  except being formed respectively between the second fluid in each cavity and part of the second support plate. The first fluid is dispensed by moving the second support plate along the side of each channel  88 ,  90 . The first fluid in each channel may be the same or different for each cavity  84 ,  86 . With a similar first fluid dispensing method as described above, regions of first fluid  92  may be formed on display areas of the second support plate. 
     The above embodiments are to be understood as illustrative examples. The example of  FIG. 5  is an example of manufacturing a display device with three layers of first fluid each for example coloured differently, whereas the example of  FIG. 6  is an alternative method of manufacturing a display device with two layers of first fluid. It is to be appreciated that further types of display device may be manufactured using the principles described above, for example using a cavity between two support plates as a second fluid reservoir and for example using a channel of first fluid for dispensing the first fluid. In some such examples, a support plate may be used having a different construction than described above; for example, a support plate with a construction more similar to that of the first support plate described above with  FIG. 1  may be used rather than the second support plate described with  FIG. 1  and vice versa. 
     In the example described using  FIG. 4 , a third roller and a fourth roller are used as part of a process for dispensing the first fluid. It is envisaged that in further examples the use of at least a surface, such as of a roller, may be used in the manner of using the third roller and optionally the fourth roller to dispense a first fluid on a support plate of an electrowetting device; in some examples such a first fluid dispensing technique may be used without dispensing the second fluid in the manner described above. In other words, these methods of dispensing the first and second fluids may be used independently of each other, in further examples. Therefore, in further examples, with reference to  FIG. 8 , a method of manufacturing an electrowetting display device comprises: providing a first support plate; providing the first fluid and the second fluid, the first fluid being provided at least partly within a channel formed by: a part of a surface of the first support plate, an interface between the first fluid and the second fluid, and a further surface; the first fluid is dispensed on the part of the surface of the first support plate by moving the part of the surface of the first support plate along a side of the channel. In some such examples, the second fluid may be provided as a reservoir of second fluid contained by a container such as a bath, with the first support plate being immersed in the bath of second fluid, rather than the second fluid reservoir being provided in a cavity between the first and second support plates, as described in examples above. In some examples, the first support plate is provided such that the part of the surface of the first support plate and a horizontal plane forms an angle of one of: between 90 degrees and 170 degrees or between 135 and 160 degrees. In accordance with some such further examples, apparatus may be used which comprises a first support plate feeding system configured to provide the first support plate having a surface; a system for providing a reservoir of the second fluid; and a further surface for example as described above, for forming a channel within which the first fluid is at least partly provided. As explained in examples above, the channel may be formed by: a part of the surface of the first support plate, an interface between first fluid in the channel and the second fluid, and the further surface. The first support plate feeding system in such examples is further configured to move the part of the surface of the first support plate along a side of the channel, to dispense the first fluid on the part of the surface of the first support plate. 
     Examples described above relate to electrowetting display devices. Further examples are envisaged for manufacturing an electrowetting device which is not a display device. 
     Further examples are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the accompanying claims.