WO2008125644A1

WO2008125644A1 - Dispensing method and device for dispensing

Info

Publication number: WO2008125644A1
Application number: PCT/EP2008/054457
Authority: WO
Inventors: Charles Richard Manuel Schmidgall; Melanie Maria Hubertina Van De Weijer-Wagemans; Robert Hayes
Original assignee: Liquavista B.V.
Priority date: 2007-04-13
Filing date: 2008-04-11
Publication date: 2008-10-23
Also published as: TWI519357B; CN101669060A; CN101669060B; GB0707201D0; TW201107047A; JP2010524039A

Abstract

Dispensing method and device for dispensing A method of providing a laye r of a first fluid on an area (2) of a surface by means of a dispenser (3) having an opening (8). The method comprises the step of providing a layer of a second fluid (7) on the surface, the second fluid being immiscible with the first fluid. It also includes the step of arranging the opening of the dispenser in the second fluid above the area and the step of dispensing the first fluid (6) through the opening assisted by a third fluid (9 ) for settling on the first area, the third fluid being immiscible with the first fluid.

Description

Dispensing method and device for dispensing

Field of the Invention

The invention relates to a method for providing a layer of a first fluid on a first area of a surface by means of a dispenser. The invention also relates to an apparatus for carrying out the method.

Background of the Invention International application WO 2005/098797 discloses a method of providing a oil layer on a surface of a substrate, particularly suitable for making electrowetting displays. The surface is initially covered by a layer of water. A dispenser has its opening in the water layer and above the surface. Oil is fed into the dispenser and a drop of oil is formed between the opening and the surface. The surface includes first hydrophobic areas surrounded by second hydrophilic areas. When the dispenser moves over the surface, the drop of oil is dragged over the first and second areas and replaces the water on the first areas by a layer of oil and leaves the water on the second areas.

A disadvantage of this method of providing an oil layer is the difficult control of the thickness of the oil layer.

An object of the invention is to provide a method that allows an easier control of the thickness of the oil layer.

Summary of the Invention The object is achieved by a method of providing a layer of a first fluid on a first area of a surface by means of a first dispenser having an opening, comprising the steps of

- providing a layer of a second fluid on the surface, the second fluid being immiscible with the first fluid; - arranging the opening of the first dispenser in the second fluid above the first area; and - dispensing the first fluid through the opening assisted for settling on the first area

- assisting the dispensing by a third fluid, the third fluid being immiscible with the first fluid. The addition of a third fluid gives an additional degree of freedom to control the deposition of the first fluid on the surface. In particular, the third fluid may be used to remove pockets of e.g. air that got trapped on the surface during the provision of the layer of the second fluid. The removal of the pockets improves the deposition of the first fluid on the surface. The immiscibility ensures that only the first fluid is deposited without inclusion of the assisting third fluid and that the effect of the third fluid is not affected by mixing with the first. The stability of the method is increased if the second and the third fluid are also immiscible.

In a first embodiment of the method the third fluid is applied using a second dispenser having an opening arranged in the second fluid. The removal of the trapped pockets may be carried out independently from the provision of the layer of the first fluid. For example, the second dispenser may be scanned over the surface one or more times, followed by one or more scans of the first dispenser. When the second and third fluid are immiscible, mixing of the second and third fluid will be avoided.

The third fluid may be applied through the opening of the second dispenser to form a globule of the third fluid between the opening and the surface. The globule appears to be effective in removing pockets of e.g. air, trapped on the surface. The second dispenser having an opening arranged in the second fluid may also be applied independently of the first dispenser and the first fluid and may be used for removing trapped pockets of e.g. air from the surface.

Although the second dispenser may precede the first dispenser in scanning the surface, advantageously the first dispenser precedes the second dispenser in scanning the surface. When the layer of the first fluid has been deposited on the surface, the trapped pockets are more likely to be removed by the globule of the third fluid than when the first fluid has not yet been deposited. Moreover, it makes the thickness of the deposited layer of the first fluid more uniform.

In a second embodiment of the method the third fluid is applied through the opening of the first dispenser. In that case the amount of the third fluid and its position can be regulated to influence the amount and the way of deposition of the first fluid. It allows an improved control of the thickness of the deposited layer of first fluid, in particular the uniformity of the thickness. In a special version of the second embodiment the method comprises the steps of

- dispensing the third fluid through the opening of the dispenser to form a globule of the third fluid between the opening and the surface; and

- dispensing the first fluid through the opening for moving along an interface between the second fluid and the third fluid and settling on the first area.

The interface between the globule of third fluid between the opening of the dispenser and the surface provides a path for the first fluid to move from the opening of the dispenser to the surface. The amount of the first fluid deposited on the first areas can be controlled by the size of the globule. A larger globule provides a thicker layer of the first fluid on the first areas. The filling can be controlled so accurately, that for many applications post-filling levelling of the deposited first layer by e.g. a doctor blade is no longer necessary. The deposition of the first fluid is improved when the first area has a lower wettability for the second fluid than for the first fluid. The difference in wettability facilitates the replacement on the surface of the second fluid by the first fluid.

The first, second and third fluid may be liquids. In a special embodiment of the method the first fluid is a first liquid, the second fluid is a second liquid and the third fluid is a gas. The interface between the gas and the second liquid forms a good-quality path for the first liquid to move from the dispenser to the surface.

When the second fluid is polar or electroconductive, the surface provided with the first and second fluid and forming part of a substrate is particularly suitable for use in a switchable optical elements, such as an electrowetting display. The gas may be air, which happens to form good globules. When the layer of second fluid is applied to the surface, either by dispensing the second fluid on the surface or by immersing the item having the surface in the second fluid, pockets of air may get trapped on the first areas because of low wettability for the second fluid. During the dispensing of the first fluid, the globule of air between the dispenser and the surface will merge with the trapped pocket, thereby releasing the pocket of air from the first area and making the entire area available for the first fluid. When the dispenser moves over the surface, the globule operates as a cleaner for trapped air pockets. The method can advantageously be used for applying a first fluid on a surface on which the first area has a neighbouring second area, the second area having a higher wettability for the second fluid than for the first fluid. Due to the difference in wettability, the first fluid will preferentially adhere to the first areas and not to the second areas. Similarly, the second fluid will remain adhered to the second areas and be driven off the first areas. As a result, the first areas will be covered by a layer of the first fluid, the thickness depending, amongst others, on the size of the globule, and the second areas will remain covered by the second fluid.

When the size of the first area is small, the deposited first fluid may assume a shape approaching a semi sphere. Such curved depositions are also covered by the term 'a layer of the first fluid' .

When a maximum dimension of the opening of the first and/or second dispenser is smaller than a minimum dimension of the first area, each area can be filled accurately to obtain the desired thickness of the first layer, which may be different for different first areas.

When a maximum dimension of the opening of the first and/or second dispenser is larger than a minimum dimension of the first area, several adjacent first areas can be filled simultaneously, which allows increasing the deposition speed. An opening having an elongate shape allows filling first areas in one sweep of the first dispenser or removal of the air by one sweep of the second dispenser. An area or a pattern of areas can be filled by step-wise or continuously moving the dispenser over the area in a grid-like pattern. Filling by sweeping an elongate dispenser over the surface requires fewer movements and can speed up the deposition process. The boundaries of the globule, i.e. the parts of the globule where the normal on the interface line between the first and second fluid on the surface is not parallel to the direction of movement, may cause local non- uniformity of the thickness of the deposited layer. The elongate dispenser allows the boundaries to be kept outside the first areas onto which the first fluid is to be deposited, thereby avoiding non-uniformity of the thickness of the deposited layer on the first areas. When the opening of the first dispenser and the surface move with respect to each other in a direction preferably substantially perpendicular to a long axis of the elongate shape, a maximum area is covered by a single sweep of the dispenser.

The method is particularly suited for depositing a first layer on a surface comprising a plurality of first areas separated by second areas and forming a pattern. A uniform thickness of the first layer is achieved when the first fluid is deposited by a dispenser having an elongate opening. Preferably, the long axis of the elongate shape of the opening has at least the same length as a dimension of the pattern parallel to the long axis. If the first fluid is deposited on a pattern in two or more sweeps and part of the globule passes over a first area twice, the thickness of the layer deposited on the first area will be different from first areas over which the globule has passed only once. Therefore, the thickness will be more uniform when the pattern is filled in one sweep of an elongate dispenser than in several sweeps of a smaller dispenser. In a special embodiment of the method a borderline between a first area and a second area and a local direction of a leading interface between the second fluid and first fluid passing over the borderline form an angle different from zero. When the leading interface between the first and/or second dispenser opening and the surface forms a line contact with a borderline between first and second areas, the fluid interface tends to pin on the borderline, causing unevenness in the thickness of the deposited layer of first fluid. When the borderline forms a non-zero angle with the interface, there is no line contact anymore but only a point contact, which hardly shows any pinning. As a result, the thickness of the deposited layer of first fluid is more uniform. An angle of 5° or more causes a noticeable improvement of the uniformity. Very good uniformity is obtained for angles of 20° and more. When the opening of the dispenser is rectangular, the local direction of the leading interface is parallel to the long axis of the opening. A rectangular pattern of first areas should therefore be arranged with its borderlines at a non-zero angle with the long axis.

The above oblique scanning is not only advantageous for a three-fluid deposition method, but also improves the uniformity of the thickness of the deposited layer for a two-fluid deposition method in which the first fluid is dispensed within the second fluid without the application of the third fluid. The advantage also applies to dispensers depositing the first fluid without the second fluid or applying the third fluid only within the second fluid. In the latter case the direction of the leading interface between the second fluid and the third fluid is relevant instead of the direction of the leading interface between the second fluid and the first fluid.

The first dispenser may be scanned once over the surface to deposit the layer of the first fluid. A greater uniformity of the thickness of the layer is achieved when the first dispenser is scanned two or more times of the surface. During the first scan the first fluid is deposited on the surface; during the following scan or scans the first fluid is redistributed over the surface, by supplementing first fluid where too little was deposited in the first scan and by removing first fluid where too much was deposited. If a first and second dispenser is used, one or more scans of the second dispenser following the first dispenser also increases the uniformity of the thickness.

The surface provided with the first and second fluid layer can be converted to a closed system when the surface is part of a first substrate and a second substrate is provided defining a space between the first substrate and the second substrate comprising the first fluid and the second fluid. A second aspect of the invention relates to an apparatus including a first dispenser having an opening for providing a layer of a first fluid on a first area of a surface using a method according to the invention.

In a first embodiment of the apparatus a second dispenser having an opening is provided for applying the third fluid.

In a second embodiment of the apparatus the first dispenser is provided with a first input for the first fluid and a second input for the third fluid, allowing the amount of first fluid and the size of the globule of third fluid to be controlled, thereby controlling the amount of first fluid deposited on the surface. In a special embodiment of the apparatus the opening of the first and/or second dispenser is elongate. The apparatus advantageously includes a movement stage for moving the dispenser and the surface with respect to each other.

When the device comprises a controller for controlling the first fluid and the third fluid, the thickness of the deposited layer of first fluid can be controlled to increase the accuracy of the thickness of the deposited layer. The controller may control the amount of the first fluid and / or the third fluid. The input for the controller may be values provided by a measurement device determining the thickness of the deposited layer or by a measurement device determining the shape and / or size of the globule of third fluid. The controller may also use manual input from an operator of the apparatus.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Fig. 1 shows an apparatus according to the invention for dispensing oil on a surface using an air globule; Fig. 2 and 3 show a dispenser for dispensing oil on a surface having a pattern;

Fig. 4 shows an apparatus having an elongate dispenser; Fig. 5 (a), (b) and (c) show a first, second and third orientation for scanning the surface;

Fig. 6 shows a cross-section of an electrowetting element;

Fig. 7 shows a controller for the apparatus; and Fig. 8 shows a dispenser for dispensing oil and a separate dispenser for applying air.

Detailed Description of the Invention

Figure 1 shows in cross-section a first embodiment of an apparatus according to the invention for dispensing a first fluid on a surface. A plate 1 has a surface 2 on which a layer of a first fluid is to be deposited. A dispenser in the form of a syringe needle 3, having a central channel 4, is moved over the surface in a direction 5. The first fluid 6 is supplied through the channel 4. The surface 2 is covered by a layer of a second fluid 7. The needle has a round opening 8, which in operation is located within the second fluid and above the surface 2. A third fluid 9 is located partly within the channel 4 and partly between the opening 4 and the surface 2. The third fluid forms a globule 10 between the opening 4 and the surface 2. The globule 10 may locally adjoin the surface 2.

The first fluid 6 moves as a relatively thin layer along the interface 11 between the second fluid 7 and the third fluid 9 from the syringe 3 to the surface 2, where it settles as a layer 12. A leading interface 13 between the second fluid 7 and the first fluid 6 pushes the second fluid away and replaces it by the first fluid. The thickness of the layer that remains on an area of the surface after passage of the dispenser depends, among others, on the width of the opening 8, its shape, the speed of movement of the dispenser, the distance between the opening 8 and the surface 2, viscosities of the fluids and the size of the globule, amount of first and third fluid, interfacial tensions of the various interfaces, and the chemical contrast, i.e. the difference in hydrophobicity between the various combinations of fluids and the surface and the dispenser. The first fluid 6 may be an alkane, such as hexadecane, or an oil, such as a hydro-carbon oil. The embodiment of Figure 1 uses a silicone oil. The second fluid 7 may be any fluid that is non-miscible with the first fluid. The second fluid may be polar or electroconductive, which is useful in some applications of the plate covered with the first and second fluid. The embodiment shown uses water as second fluid. The third fluid 9 is advantageously immiscible with both the first fluid and the second fluid to stabilise the globule. The third fluid may be a gas, such as air, nitrogen or argon. The embodiment uses air as third fluid. Other immiscible fluids that can be used are fluorocarbon and liquid metals such as mercury.

The deposition of the first fluid on the surface will be facilitated if the surface has a higher wettability for the first fluid than for the second fluid. In the embodiment shown, the plate 1 can be covered by a hydrophobic layer, e.g. an amorphous fluoropolymer such as AF 1600. The hydrophobic layer increases the tendency of the oil to adhere to the surface and repel the water.

The application of the third fluid as shown in Figure 1 can be achieved by the following subsequent steps: filling the syringe with the first fluid, pulling a quantity of air into the syringe, inserting the syringe into the layer of the second fluid 7, and pushing fluid out of the syringe. The size of the globule is determined by the amount of air in the syringe and the properties of the first and second fluids. The syringe may be replaced by a reservoir filled with first liquid and a pump mechanism for dispensing the desired amount of first liquid. Figure 2 shows a top view of a dispenser for dispensing the first fluid on a surface having a pattern. The pattern 20 comprises first areas 21, in this embodiment squares, having a greater wettability for the first fluid 6 than for the second fluid 7. The squares may be made of a layer of AF1600. A neighbouring second area 22 has a greater wettability for the second fluid than for the first fluid. The area 22 may be made of a layer of a variety of materials, including a photoresist, such as SU8. The maximum dimension of the opening 8 of the needle in the Figure is smaller than a minimum dimension of the square. The size of the needle allows filling of only selected first areas of the pattern. When depositing the first fluid on the first area, the extent of the layer of first fluid is limited by the second area, which repels the first fluid. The second area may be formed by arranging a separate layer having the form of the second area on an uninterrupted layer that forms the first areas. When the first area is hydrophobic, the separate layer should be hydrophilic. The separate layer may be formed by e.g. a printing method or evaporation. The second area may also be formed by walls having a height, which mechanically restrain the first fluid to the first area.

Figure 3 shows also a top view of a dispenser for dispensing the first fluid on a surface having a pattern. The pattern 30 includes first areas 31 and second areas 32. The needle 33 has an opening 34, which has a maximum dimension, i.e. a diameter, larger than a minimum dimension of the first area, i.e. the length of a side of the first area. When the opening is moved over the pattern on the surface, a plurality of first areas is covered by the first fluid simultaneously, thereby increasing the deposition speed of the apparatus. The first fluid preferentially adjoins the first areas and is repelled by the second area because of their different wettabilities.

The deposition of the first fluid through the layer of second fluid has several advantages. It reduces the spilling of first fluid. It reduces the contamination of the surface from the environment; contaminants tend not to pass the barrier of environment to second fluid. The presence of the second fluid makes it easier to localize the deposition. The second fluid causes the first fluid to be less exposed to oxygen in the air, which reduces oxidation of the first fluid. If the first fluid were deposited without the presence of the second fluid layer, the first fluid would get pinned to impurities on the second area. When the second fluid is in contact with the second area before the deposition of the first fluid, the first fluid is less likely to get pinned on the impurities, because it has to repel the second fluid from a small area around the impurity.

During the application of the layer of second fluid on the surface, air may get trapped on the surface, in particular on first areas near the border with a second area. When the dispenser is swept over the first area and the globule is filled with air, the trapped air will merge with the globule and its place on the first area will be occupied by the first fluid. The globule operates as an air cleaner of the surface. After the deposition of the first fluid on the surface, the plate with first and second fluid may be used in e.g. an electrowetting device, such as a display device, an optical element, an adjustable diaphragm or an adjustable lens. The second fluid may also be removed after the deposition of the first fluid and the plate with only the first fluid used in an application.

Figure 4 shows an apparatus having an elongate dispenser for depositing a layer of a first fluid oil through a layer of a second fluid water provided on the surface and assisted by a third fluid air. The figure shows a cut through the dispenser and the plate. The dispenser may be closed at the short sides by two vertical walls. The dispenser 40 has the shape of a U with its opening 41 facing the surface 42 of a plate 43. The opening is below the surface of the second fluid. The interface between the second fluid and the environment is not shown in the Figure. The dispenser has a first input in the form of a tube 44 for feeding the oil into the dispenser and a second input in the form of a tube 45 for controlling the air. A long dispenser may have two or more first inputs and/or second inputs, regularly spaced of the length of the dispenser to improve the control of the fluids. The air forms an elongate globule 46 surrounded by a layer of oil 47. The width of the opening 41 is preferably smaller than 10 mm, e.g. 2 mm. When the opening is wider than 10 mm, oil tends to escape from the opening and move up in the water. The distance of the opening above the surface is preferably smaller than 2 mm, and is 0.1 mm in a special embodiment. A small opening facilitates filling of the dispenser by the first fluid through capillary forces. The dispenser has a hydrophobic surface on the inside walls 48 and on the wall parts 49 adjacent the opening 41. The hydrophobic character pins the oil to the dispenser. The outer walls 50 of the dispenser, which are at least partly adjoined by water, are hydrophilic to avoid contamination with oil. The dispenser may be made of PMMA, which is slightly hydrophobic. This material has the advantage of a high contact angle hysteresis, which improves the positional stability of the oil. Although the first fluid in the figure pins on the two outer edges of the wall part, it may also pin on the two inner edges of the wall part. Hysteresis refers to the difference in contact angle after advancing and receding motion of the fluid boundary. During the deposition process the dispenser is moved in a direction 51, substantially perpendicular to the long axis of the opening 41, thereby moving a leading interface 52 between the water and the oil over the surface 42. The surface comprises a pattern of areas 53, each of which may be a first area or a sub-pattern of first areas and second areas. For example, each sub-pattern may be a display device, and two or more display devices are arranged on the surface in a direction parallel to the long axis of the dispenser. Furthermore, a pattern or sub-pattern may have a shape that conveys a meaning to an observer, such as a logo. Such a sub-pattern may be combined with another sub-pattern for a display function, together providing a signage function. In a display device the pattern or sub-pattern may be switchable as a common display element or permanent, i.e. non- switchable. In another embodiment, such a pattern or sub-pattern provides a decorative effect, for example to enhance the viewer experience.

The length of the opening is substantially the same as or larger than the dimension of the pattern parallel to the long axis of the opening. The length should be at least so large that any deposition irregularities caused at the boundary of the globule 46 occur outside the pattern. The length of the opening may by substantially equal to the size of the surface in the direction perpendicular to the scan direction. The area between the areas 53 is preferably hydrophilic, e.g. covered with SU8, to avoid deposition of oil in this area of the surface.

In the embodiment of the apparatus shown in Figure 4, the leading interface 52 of the oil runs parallel to borderlines 54 between first areas and second areas. Since the oil 47 does not want to adjoin second areas, the shape of the oil below the dispenser is disturbed along the contact line from hydrophobic to hydrophilic areas. The pinning of the oil on the borderlines causes a stick-slip motion during the movement of the dispenser over the surface, which may result in a striped deposited oil layer.

Figure 5(a) shows a first orientation of the dispenser 60 with respect to a surface having a pattern 61 of first and second areas arranged on a plate 62. The direction of scanning is indicated by arrow 63. The first orientation is the same as the orientation shown in Figure 4. Figure 5(b) shows a second orientation, in which the plate 62 together with the pattern 61 is rotated over an angle of approximately 8 degrees compared to the orientation in Figure 5 (a). The leading interface 52 of the dispenser is now at the same angle of 8 degrees with the borderline 54. Since the interface and the borderline have no longer a line contact but only a point contact, the pinning effect is strongly reduced and the thickness of the deposited layer is more uniform than in the case of Figure 5(a). An improvement of uniformity is observed for angles larger than 5 degrees and for angles larger than 22.5 degrees the uniformity does not improve further noticeably. Figure 5(c) shows an alternative configuration, wherein the plate 63 has one of its edges parallel to the dispenser 60 and the pattern 64 has borderlines at an angle unequal to zero with the leading interface of the dispenser. The leading interface for a straight, elongate dispenser is straight and has a direction equal to that of the long axis of the dispenser opening. When the opening of the dispenser is curved in a plane parallel to the surface, the leading interface will also be curved. To avoid the above stick- slip motion, the local direction of the leading interface should form a non-zero angle with the direction of the borderlines.

Although the oblique filling as shown in Figures 5(b) and (c) is described for a filling process using three fluids, it is also advantageous for filling methods where the first fluid is dispensed on the surface within a second fluid, since similar stick-slip motion occurs in this case. The oblique filling is similarly advantageous in a one-fluid filling method, in which one fluid is deposited on the surface in air or vacuum.

Figure 6 shows a cross-section of a series of electrowetting elements made using the deposition method according to the invention. A first substrate 70 is provided with electrodes 71, deposited as a thin-film conductor on the substrate. Each electrode is connected to a signal line 72 for providing a voltage. The electrodes are covered by a thin hydrophobic layer 73 of the amorphous fluoropolymer AF1600. A pattern of a thin hydrophilic layer 74 of SU8 divides the surface of the substrate in hydrophobic first areas 75 between the hydrophilic second areas 74. The size of the first areas is 160 micrometers square, the second areas have a width of 10 micrometers and a height of 3 to 6 micrometer. The first substrate 70, provided with the layers 71, 73 and 74, is subjected to the deposition method according to the invention using oil as first fluid, water as second fluid and air as third fluid or another combination of fluids. After carrying out the method the first areas 75 are uniformly covered by an oil layer 76 having a thickness of between 3 and 6 micrometer, for example 5 micrometer. The second areas 74 and the oil layer are covered by water 77. The water may contain salt to increase its electrical conductivity and to enlarge the temperature window for the method. The second fluid, water in this example, used during the method is preferably the same fluid used in the product that includes the substrate, which avoids changing the second fluid after the execution of the method by another fluid. A second substrate 78 forms a closed space between the first and second substrate. The space is protected from the environment by seals, not shown in the Figure, attached to both substrates.

The pattern of the layer 74 defines elements on the substrate to which the oil layer 76 is confined. Each element has an electrode 71. Another electrode 79, connected to a signal line 80, is in contact with the water 77, forming a common electrode for a plurality of elements. When a voltage is applied between the common electrode 79 and the electrode 71 of an element, the oil layer 76 in that element moves to the side of an element or breaks up and the first surface will at least partly be covered by the water 77. This so-called electro wetting effect is more fully described in international patent application WO03/071346. When the oil and / or the water has specific optical properties for absorption, reflection and / or transmission of light, the element can operate as a light valve in e.g. a display.

The electrowetting elements may be used in a display apparatus, in which a plurality of electrowetting elements forms a display device. A display driving system in the apparatus provides the voltages for setting the elements in the desired state.

Figure 7 shows an apparatus for depositing a layer on a surface according to the invention. A tray 82 can be filled with the second fluid. The tray contains a stage 84 on which a substrate can be arranged. A dispenser 85, having an opening 86 at the lower side, is mounted on a translation stage, not shown in the Figure, that enables the dispenser to sweep over the stage 84. Alternatively, the dispenser is fixed and the surface is mounted on a translation stage. In operation the dispenser opening is below the level of the second fluid. A first container 87 for the first fluid is connected to a first control unit 88, e.g. a valve or a pump, that controls the amount of first fluid to be delivered to the dispenser 85 via a connection 89. A second container 90 for the third fluid is similarly connected to a second control unit 91 for delivering the third fluid to the dispenser via a connection 92. When the third fluid is air, the second container may be dispensed with and the control unit 91 can withdraw the air from the surroundings, preferably via a filter, or exhaust any superfluous air. The connection 92 may also be used to exhaust air from the dispenser when the size of the globule must be reduced or when the air removed from the pockets becomes substantial.

A controller 93 provides signals for setting the first and second controller to the desired settings. The apparatus may include a measurement device for determining the thickness of the deposited layer. The thickness value may be used as input for setting the control units. The apparatus may also include a device for measuring the shape and / or the size of the globule of third fluid or the volume of first fluid between the dispenser and the surface, e.g. using a camera observing the dispenser in the direction of its long axis, and use this input for setting the control units. The height of the dispenser above the surface may be kept at a desired value, for example by measuring the height at the two far ends of the elongate dispenser and maintaining these at equal values. The controller may also use manual input from an operator of the apparatus instead of measured values.

Figure 8 shows an alternative embodiment of the method according to the invention. A dispenser 100 filled with the first fluid 6 through a tube 101 and having an opening in a layer of second fluid 7 is scanned in a direction 102 over the surface 42 of the plate 43, depositing a layer 103 of the first fluid on the surface. A dispenser 105 filled with the third fluid 9 through a tube 106 and having an opening in the layer of second fluid 7 scans the surface 42 in a direction 107, following the dispenser 100. The third fluid forms a globule between the opening of the dispenser 105 and the surface 42. The globule removes pockets of air trapped on the surface after the provision of the layer of the second fluid on the surface.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention 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 invention, which is defined in the accompanying claims.

Claims

1 A method of providing a layer of a first fluid on a first area of a surface by means of a first dispenser having an opening, comprising the steps of - providing a layer of a second fluid on the surface, the second fluid being immiscible with the first fluid;

- arranging the opening of the first dispenser in the second fluid above the first area; and

- dispensing the first fluid through the opening for settling on the first area, - assisting the dispensing by a third fluid, the third fluid being immiscible with the first fluid.

2 A method according to claim 1, using a second dispenser having an opening arranged in the second fluid for applying the third fluid.

3 A method according to claim 2, comprising the step of applying the third fluid through the opening of the second dispenser to form a globule of the third fluid between the opening and the surface.

4 A method according to claim 2 or 3, wherein the first dispenser precedes the second dispenser in scanning the surface.

5 A method according to claim 1, wherein the third fluid is applied through the opening of the first dispenser.

6 A method according to claim 5, comprising the steps of

- dispensing the third fluid through the opening to form a globule of the third fluid between the opening and the surface; and

- dispensing the first fluid through the opening for moving along an interface between the second fluid and the third fluid and settling on the first area. 7 A method according to claim 1, wherein the first area has a lower wettability for the second fluid than for the first fluid.

8 A method according to claim 1, wherein the first fluid and the second fluid are liquids and the third fluid is a gas.

9 A method according to claim 8, wherein the second fluid is polar or electroconductive .

10 A method according to claim 8, wherein the gas is air.

11 A method according to claim 1, wherein the first area has a neighbouring second area, the second area having a higher wettability for the second fluid than for the first fluid.

12 A method according to claim 11, wherein the surface comprises a plurality of first areas separated by second areas and forming a pattern.

13 A method according to claim 12, wherein the pattern or a sub-pattern of the pattern has a decorative function or acts as a signage.

14 A method according to claim 1, 2 or 5, wherein a maximum dimension of the opening of the dispenser is smaller than a minimum dimension of the first area.

15 A method according to claim 1, 2 or 5 wherein a maximum dimension of the opening of the dispenser is larger than a minimum dimension of the first area..

16 A method according to claim 1, 2, 5 or 15, wherein the opening of the dispenser has an elongate shape. 17 A method according to claim 16, wherein the opening and the surface move with respect to each other in a direction substantially perpendicular to a long axis of the elongate shape.

18 A method according to claim 17, wherein the surface comprises a plurality of first areas separated by second areas and forming a pattern, and the long axis of the elongate shape has at least the same length as a dimension of the pattern parallel to the long axis.

19 A method according to claim 16, wherein a borderline between a first area and a second area and a local direction of a leading interface between the second fluid and first fluid passing over the borderline form an angle different from zero.

20 A method according to claim 1, including the step of scanning the first dispenser one or more times over the surface.

21 A method according to claim 1, wherein the surface is part of a first substrate and the method includes the step of providing a second substrate defining a space between the first substrate and the second substrate comprising the first fluid and the second fluid.

22 A method according to claim 21, wherein the first substrate and the second substrate form an electrowetting element.

23 An apparatus including a first dispenser having an opening for providing a layer of a first fluid on a first area of a surface using a method according to any one of the claims 1 to 22.

24 An apparatus according to claim 23, including a second dispenser having an opening for applying the third fluid. 25 An apparatus according to claim 23, the first dispenser being provided with a first input for the first fluid and a second input for the third fluid.

26 An apparatus according to claim 23, 24 or 25, wherein the opening of the dispenser is elongate.

27 An apparatus according to claim 23, 24 or 25, including a movement stage for moving the dispenser and the surface with respect to each other.

28 An apparatus according to claim 23, 24 or 25, including a controller for controlling the first fluid and the third fluid.

29 An apparatus according to claim 23, 24 or 25, including a controller for controlling a height of the dispenser above the surface.