WO2014163504A1

WO2014163504A1 - Electrowetting optical element

Info

Publication number: WO2014163504A1
Application number: PCT/NL2014/050215
Authority: WO
Inventors: Hermanus Feil
Original assignee: Miortech Holding B.V.
Priority date: 2013-04-05
Filing date: 2014-04-07
Publication date: 2014-10-09
Also published as: NL2010578C2

Abstract

An electrowetting optical element and a method of manufacturing of such element is provided, comprising a second electrode layer stack and a first electrode layer stack, and a containment space formed between said second electrode layer stack and said first electrode layer stack said containment space at least containing a polar liquid and a non-polar liquid, the polar and non-polar liquids being immiscible with each other. Said electrowetting optical element further comprises at least one cell wall extending between said first and second electrode stacks for defining sides of said containment space. Said first electrode layer stack and said second electrode layer stack comprises a first and second electrode layer respectively for applying a voltage to said electrodes for allowing rearranging said polar liquid relative to said non-polar liquid. Said at least one cell wall having a surface interfacing said containment space and a cell wall end face. Said cell wall interface surface has a hydrophobic surface portion interfacing said containment space at an end portion of said cell wall.

Description

TITLE: Electrowetting optical element

FI ELD OF THE I NVENTION

The present invention relates to an electrowetting optical element, a display comprising electrowetting optical elements and a method of manufacturing an electrowetting optical element.

BACKGROU ND

Electrowetting technology is based on modification of an energy balance between on one hand surface tension forces of liquids and wetting properties of a solid surface, and on the other hand electrostatic forces induced by an applied voltage over a capacitor arrangement comprising said boundary layer.

In accordance with international patent application WO2012055724 an electrowetting optical element may comprise a first electrode layer stack and a second electrode layer stack, and a containment space formed between said second electrode layer stack and the first electrode layer stack, at least one cell wall extending between the first and second electrode stacks, for defining sides of the containment space, the containment space at least containing a polar liquid and a non- polar liquid, the polar and non-polar liquids being immiscible with each other.

The second electrode layer stack comprises a substrate, a second electrode layer and an insulating layer having a hydrophobic interface surface with said containment space, and said first electrode layer stack comprises a superstrate and a first electrode layer having a second interface surface with said containment space. Said hydrophobic interface surface has a higher hydrophobicity than the second interface surface.

The cell walls are fixedly mounted on said second interface surface of said first electrode layer stack and extend towards said second electrode layer, wherein an end face of said at least one cell wall opposite said second electrode layer stack faces said hydrophobic interface surface in a loose manner. No fixation or structural attachment is achieved of the end face of the cell walls with the hydrophobic interface of the second electrode layer stack. This end face may be, but is not necessarily, contiguous to the hydrophobic surface of the second electrode layer stack. Furthermore, a slit may be present in between the end face of the cell walls and the hydrophobic interface for entrainment of the non-polar liquid into the slit. The electrowetting element is arranged for enabling powering of said first and second electrode layer stacks for rearranging said polar liquid relative to said non- polar liquid. In an unpowered state, i.e. when no voltage is applied over the first and second electrode, the lowest energetic state of the system is where the non-polar liquid forms a boundary layer between the polar liquid and the hydrophobic surface of the insulating layer. This is because the polar liquid is repelled by the hydrophobic layer. The poor transmissibility of the non-polar liquid then forms an obstruction to light that penetrates the system.

When a voltage is applied over the electrodes, the lowest energetic state of the system becomes the situation wherein the (poorly conductive or insulating) non-polar liquid is pushed aside by the (conductive) polar liquid, and the polar liquid thereby is in direct contact with the insulating hydrophobic layer. Note that the voltage must be large enough for the electrostatic forces to overcome the repellent and surface tension forces that separate the polar liquid from the hydrophobic surface. In this situation, light that penetrates the system has rather unobstructed access to the insulating hydrophobic layer because of the well transmissibility of the polar liquid and the non-polar liquid being pushed aside. In the powered up state, when voltage is applied over the electrodes, the electrowetting element is thus transmissive. This working principle is used in electrowetting type displays and screens.

The cell walls extending towards the second electrode layer cause the interface surface between the polar liquid and the non-polar liquid to be curved in a convex meniscus shape when the electrowetting optical element is in an unpowered state. This causes the electrowetting optical element to be more transparent at the edges of the element near the cell walls. Incident light from the first electrode layer will then be reflected more near the cell walls than incident light at the center of the electrowetting element. This causes uneven light distribution over each electrowetting optical element and over a display comprising a plurality of concatenated electrowetting optical elements. The uneven distribution or obscuration of light is all the more evident from light passing through an electrowetting optical element from the second electrode layer to the first electrode layer due to the convex meniscus shaped interface surface between the polar and non-polar liquids.

International patent application WO2012/039471 describes an electrowetting display, wherein each of a pair of substrates that configure one cell has a drive unit. The electrowetting display is configured by bonding together a first substrate, which contains a first hydrophobic liquid material in a region surrounded by a first pixel wall, and a second substrate, which contains a second hydrophobic liquid material in a region surrounded by a second pixel wall, with a hydrophilic material between the substrates. Although it is known that a cell wall end face can be provided with a hydrophobic layer or surface, it has experimentally established that a convex or concave meniscus shaped interface surface will be formed due to capillary action where an entire cell wall interface with a containment space having a polar and non- polar liquid between electrowetting elements is either hydrophilic or hydrophobic.

SUMMARY OF THE I NVENTION

One or more of the above mentioned problems are solved according to an aspect of the invention wherein an electrowetting optical element is provided, comprising a second electrode layer stack and a first electrode layer stack, and a containment space formed between said second electrode layer stack and said first electrode layer stack said containment space at least containing a polar liquid and a non-polar liquid, the polar and non-polar liquids being immiscible with each other.

Said electrowetting optical element further comprises at least one cell wall extending between said first and second electrode stacks for defining sides of said containment space. Said first electrode layer stack and said second electrode layer stack comprises a first and second electrode layer respectively for applying a voltage to said electrodes for allowing rearranging said polar liquid relative to said non-polar liquid. Said at least one cell wall having a surface interfacing said containment space and a cell wall end face. Said cell wall interface surface has a hydrophobic surface portion interfacing said containment space at an end portion of said cell wall.

The hydrophobic end portion of the cell wall interface surface allows in an unpowered state of the electrowetting optical element, i.e. no voltage is applied to the first and second electrode layers respectively, the non-polar liquid to cover a portion of the cell wall interface surface which would have otherwise been in contact with the polar liquid. Thus it is achieved that the interface surface between the polar and non-polar liquids is distributed more even in a cross section of the electrowetting optical element and form a flat interface between both liquids. Incident reflected or transmitted light will in this state be obscured evenly across said interface surface. The electrowetting optical element or a display manufactured from concatenated electrowetting optical elements according to the invention now shows a constant, even distribution, i.e. obscuration of light. Said cell wall end face is preferably provided with a hydrophobic surface. Said hydrophobic surface portion is preferably circumferentially arranged around said end portion of said cell wall. This improves a more even distribution of the non-polar liquid around the end portion of said cell walls.

In an further preferred embodiment said hydrophobic surface portion and said hydrophobic cell wall end surface form a cap shaped hydrophobic surface portion around an end portion of said cell wall facing said second electrode layer.

This allows the non-polar liquid to be entrained in said slit more easily, preventing polar liquid to enter the slit and preventing non-polar liquid to be exchanged between adjacent electrowetting optical elements.

According to another aspect of the invention a method of manufacturing an electrowetting optical element is provided, said method comprising:

- providing a first electrode layer stack, said first electrode layer stack having a first electrode layer, and

- forming at least one cell wall extending from said first electrode stack for defining sides of a containment space, said at least one cell wall having a cell wall interface surface interfacing said containment space and a cell wall end face at an end of said cell wall opposite said first electrode layer stack,

- forming an hydrophobic surface portion at an end portion of said cell wall interfacing said containment space,

- filling said containment space with at least a polar liquid and a non- polar liquid, said polar and non-polar liquids being immiscible with each other,

- providing a second electrode layer stack, covering said containment space leaving a slit between said cell wall end face and said second electrode layer stack, said second electrode layer stack having a second electrode layer for allowing a voltage to be applied to said first and second electrode layers respectively for rearranging said polar liquid relative to said non-polar liquid.

This allows the non-polar liquid to cover a portion of the cell wall interface surface which would have otherwise been in contact with the polar liquid. Thus it is achieved that the interface surface between the polar and non-polar liquids is distributed more even in a cross section of the electrowetting optical element and form a flat interface between both liquids.

In an embodiment the method further comprises:

- applying a hydrophobic compound to said cell wall interface surface at said end portion of said pixel wall prior to said step of filling for forming a hydrophobic surface portion interfacing said containment space at said end portion of said cell wall.

In an embodiment, said step of applying a hydrophobic compound to said cell wall interface surface comprises:

- applying said hydrophobic compound to said cell wall end face using an excess amount of hydrophobic compound;

- allowing said excess hydrophobic compound to spill over to said surface at said end portion of said cell wall such that at said end portion of said cell wall is covered with the hydrophobic compound during a time period depending on de viscosity of said hydrophobic compound and a length of said end portion to be covered with said hydrophobic compound.

This allows the hydrophobic surface portion of be formed without having to apply the hydrophobic compound to the surface end portion of the pixel wall interfacing the containment space directly.

Said hydrophobic compound is subsequently cured. This allows the hydrophobic surface portion to become stable and resistant to chemical interaction with the polar and/or non-polar liquids.

BRI EF DESCRI PTION OF TH E DRAWI NG

The invention will further be described with reference to the enclosed drawing wherein embodiment of the invention is illustrated, and wherein

Figures 1 a - 1 d illustrate simplified electrowetting optical elements in accordance with the state of the art;

Figure 1 e illustrate an electrowetting optical element in accordance with the state of the art;

Figure 2a illustrates an electrowetting optical element in accordance with an embodiment of the invention;

Figure 2b shows a detail of the electrowetting optical element of fig. 2a. Figure 3 shows a block diagram of a method of manufacturing an electrowetting optical element according to an embodiment of the invention.

DETAI LED DESCRI PTION

Figures 1 a-1 d show simplified electrowetting elements 1 in an unpowered state according to the state of the art illustrating the technical problem to be solved. Figures 1 a and 1 b show an electrowetting element having a first electrode layer stack 5 and a second electrode layer stack 3, a containment space 25 defined by the first and second electrode layer stacks 3, 5 and cell walls 19 formed on the second electrode layer stack 3 extending to the first electrode layer 5. A gap or slit 32 may be formed between end faces of the cell walls 19 and the first electrode layer 5. The containment space 25 is filled with a polar liquid 29 and a non-polar liquid 30 which are immiscible with each other.

In figure 1 a the pixel walls 19 have a surface interface with the containment space 25, i.e. the polar liquid 29, which is hydrophilic. As a consequence the non-polar liquid 30 has a convex meniscus shaped interface surface with the non-polar liquid 29. For the same type electrowetting element shown in figure 1 b, however having pixel walls 19 with a hydrophobic interface surface with the containment space, the non-polar liquid 30 has a concave meniscus shaped interface surface with the polar liquid 29.

Figure 1 c and figure 1 d show electrowetting elements 1 comprising a first electrode layer stack 5 and a second electrode layer stack 3 and pixel walls 19 extending from the first electrode layer stack 5 towards the second electrode layer stack 3 showing a slit 32 between the pixel wall 19 end faces and the second electrode layer stack 3. In figure 1 c, the pixel walls 19 have a hydrophilic interface surface with the containment space 25. This causes the polar liquid 30 to have a convex meniscus shaped interface surface with the polar liquid 29.

In figure 1 d, the pixel walls 19 have a hydrophobic interface surface the containment space 25 causing a concave meniscus shaped interface surface of the non-polar liquid 30 with the polar liquid 29. As a consequence of the meniscus shape of the interface between the polar liquid 29 and non-polar liquid 30 the distribution of the non-polar liquid 3- is uneven. As it is normally the non-polar liquid 30 which is opaque, blocking light from passing through, an light leakage occurs at the electrowetting element boundaries or cell walls or at the centre of the electrowetting element.

Figure 1 e shows an electrowetting element 1 according to the state of the art in a powered state. The electrowetting element 1 may be situated between adjacent electrowetting elements, as illustrated. In the electrowetting element 1 , a containment space 25 is present between a first electrode layer stack 5, a second electrode layer stack 3 and a cell wall 19, formed on the first electrode layer stack 5. The containment space 25 is filled with a polar liquid 29 and a non-polar liquid 30. The polar liquid 29 is preferably non-aqueous polar liquid, for example comprising ethylene glycol or glycerol or a mixture thereof. Water is also a polar liquid but is less suitable for use in an electrowetting optical element due to corrosion risk of electrode layers coming in contact with the water. For the non-polar liquid 30 an oil like substance such as a silicone oil or silicone oil blend can be used. Non-polar liquid 30 is preferably opaque, enabling the electrowetting optical element to block incident light 2 from passing through or from being reflected by an optional reflective layer 14. This can be achieved for example by choosing a suitable opaque non-polar liquid 30 compound and/or by adding a colorant or pigment to the non-polar liquid.

The second electrode layer stack 3 comprises a substrate 1 1 , an insulating layer 12, a second electrode layer 13 and optional reflective layer 14 that will be described below. The second electrode layer 13 is formed of an electrically conducting material such as indium tin oxide (ITO) and has a hydrophobic interface surface 10 forming the interface with the containment space 25. The second electrode layer 13 is connectable to a first pole of a voltage source for controlling operation of the electrowetting element 1 . The hydrophobic interface surface 10 can be formed by a applying a suitable hydrophobic compound such as a fluoropolymer, for example CYTOPTM or AF1600TM to the interface surface 10.

The first electrode layer stack 5 comprises a superstrate 7 and a first electrode layer supported by the superstrate 7. The first electrode layer 6 may be in contact with polar liquid 29, the first electrode layer 6 having a less hydrophobic or hydrophilic interface surface. The first electrode layer 6 is formed by a layer of transparent conductive material such as ITO or any other suitable transparent conducting material. Also a conductive organic material known in the art have lower hydrophobic properties than the hydrophobic first interface surface 10 can be used.

The first electrode layer 6 must contact the polar liquid 29 in the electrowetting element 1 , but does not necessarily have to be a contiguous layer as shown in figure 1 e. It is sufficient if it covers at least a part of the containment space 25. The first electrode layer is connectable to another pole of the voltage source.

The first and second electrode layer 6, 13, being connectable to the voltage source, together allow the electrowetting element 1 to be powered on and off by applying an appropriate voltage to them. In an unpowered state non-polar liquid 30 will adhere to the hydrophobic interface surface 10 of the second electrode layer stack 3. Thus incident light 2 is blocked and is not allowed to pass through the electrowetting cell 1 . In a powered state, when a voltage is applied to the first and 20 second electrode layers 6, 13, the polar liquid 29 is electrostatically drawn to the hydrophobic interface surface 10, pushing the non-polar liquid 30 aside to the cell walls 21 . Incident light 2 is now allowed to pass through the electrowetting element 1 . The superstrate layer 7 and substrate layer 1 1 may be formed by any suitable material. These layers 7, 1 1 may for example be formed by a transparent glass layer, and dependent on whether the electrowetting optical cell is of the transparent type or reflective type, the substrate layer 1 1 may be formed by a non- transparent layer as well. Alternatively, superstrate layer 7 and substrate layer 1 1 may be formed from a rigid or flexible polymer material such as polyethersulfone (PES), polyimide (PI), polythiophene (PT), phenol novolac (PN), or polycarbonate (PC).

The optionally reflective layer 14 allows the electrowetting element 1 to be used in a reflective manner having light 2 incident on the superstrate side or the side of the first electrode layer stack 5 of the element 1 being reflected by the reflecting layer 14 and exiting again through the first electrode layer stack 5 side. The reflective layer 14 can be made from a metal such as aluminium, deposited on the substrate 1 1 . In reflective type electrowetting elements, the reflective layer 14 may also act as second electrode layer.

The electrically insulating layer 12 can be formed of for example silicon dioxide or aluminium oxide or any other suitable material which prevents a short circuit in applying the electrical voltage and allows an electrical field to build up such that the polar liquid is attracted to the second electrode layer 13, driving the non- polar liquid aside.

Cell walls 19 which can be for example made from acryl or acrylic material, are fixedly mounted on the less hydrophobic or hydrophilic surface of the first electrode layer 6. As a result of the mounting of the cell walls 19 on the first electrode layer, and due to the physical properties of the less hydrophobic surface, a strong mechanical connection between the cell walls 19 and the hydrophilic surface interface 6 is achieved. This results in a good structural integrity of the cell walls as mounted on the first electrode layer stack 5.

The cell walls 19, and the first and second electrode layer stacks 3 and 5 respectively, define the containment space 25 of the electrowetting optical cell 1 . The containment space 25 is filled with a polar liquid 29 and a non-polar liquid 30. The polar liquid 29 and non-polar liquid 30 are immiscible with each other. In addition, the polar liquid 29 is formed of a substance having molecules with non-zero chemical polarity. The non-polar liquid is formed of a substance having molecules with negligible or very small chemical polarity. As a result, switching of the electrodes in the powered up and powered off state modifies the balance of forces between the non-polar liquid and the polar liquid and the hydrophobic surface, causing these liquids to rearrange suitably for opening and closing the electrowetting optical cell.

The cell walls 19 can be dimensioned such that they span the distance between the first electrode layer stack 5 and the second electrode layer stack 3. This way, the cell walls 19 prevent spreading of the non-polar liquid 30 to adjacent electrowetting elements.

The cell walls 19 may comprise end faces 34 opposite the hydrophobic surface 10 of the second electrode layer 3. In figure 1 e a small slit 32 is shown in between the end faces 34 and the hydrophobic surface layer 10 of the second electrode layer 12. This enables the non-polar liquid 30 to entrain the slits 32, and to form a small interface 24 on the other side of the slit near the edge of the cell walls 19 resulting from capillary action within the slit 32. An effect of the small capillary interface is that it greatly reduces the amount of light scattering caused by the cell walls 19 in the electrowetting optical cell 1 . The capillary action can be further improved by providing the end faces 34 with a hydrophobic surface. The non-polar liquid 30 is consequently drawn more easily into slit 32.

Fig. 1 e shows the electrowetting element 1 in an unpowered state, i.e. no voltage is applied between the first and second electrode layers 13, 6. With the cell walls having a neutral or hydrophobic end face surface 34, the non-polar liquid tends to form a convex meniscus shaped surface 38 due to the surface tension of the polar liquid 29, the capillary action to the non polar liquid 30 of the slit 32 and the less hydrophobic or hydrophilic properties of the cell wall surface 21 , which tends to keep the non polar liquid 30 away from the cell wall surface 21.

Figure 2a shows the electrowetting cell 1 of figure 1 e also in an unpowered state, wherein the cell wall interface surfaces 21 at their end portions provided with a hydrophobic portion 35 interface the containment space. Such a hydrophobic portion can be formed by applying a hydrophobic compound such as a fluoropolymer, like in hydrophobic interface surface 10, to the end portion of the cell wall interface surface 21 at the end of the pixel wall 19 facing the second electrode layer stack opposite the slit 32.

Figure 2a shows the electrowetting cell 1 of figure 3 wherein the cell wall end faces 34 are at their end portions provided with a hydrophobic surface interfacing the containment space. Such a hydrophobic portion can be formed by for example applying a fluoropolymer such as CYTOPTM or AF1600TM , as in the hydrophobic interface surface 10, to the cell wall end faces 34 at the end of the pixel wall 19 facing the second electrode layer stack opposite the slit 32 and to the surface 21 interfacing the containment space 25 near the end portion of the cell wall 19.

Figure 2b show an enlarged cross section of the cell wall 19 of fig. 2a with the hydrophobic compound applied to the end portion, such that an end face 34 and surface 21 at the end portion 35 of the cell wall 19 are now hydrophobic. Both hydrophobic surface portion 35 and hydrophobic end face form a hydrophobic cap 34, 35 over the end portion of the cell wall 19.

Fig. 3 shows a method of manufacturing an electrowetting optical element in accordance with fig. 2.

In step 301 a first electrode stack 5 is provided comprising a first electrode layer (6).

In step 302 at least one cell wall 19 is formed extending from the first electrode stack. The cell walls 19 define sides of a containment space 25. The cell walls 19 have a cell wall interface surface 21 interfacing the containment space 25 and a cell wall end face 34 at an end of the cell wall 19 opposite said first electrode layer stack 5. Cell walls 19 can for example be provided by applying a layer of photo resist lacquer i.e. an acrylic compound, curing and subsequently etching this layer in a desired shape such that the cell walls 19 remain. A cell wall 19 when viewed from above can form a continuous barrier surrounding containment space 25, such that polar liquid 29 of an electrowetting optical element 1 is trapped within the cell wall 19.

In step 303, a hydrophobic end portion of the cell wall 19 is formed. To this end, a hydrophobic compound, such as a fluoropolymer, is applied to the cell wall interface surface 21 of end face 34 of the cell wall 19.

The hydrophobic compound can be applied to the cell wall end face 34 of the at least one pixel wall 19 facing the second electrode layer stack 3 opposite the slit 32. The applying can be achieved by for example using a printing process, such as flexographic printing. This is a process well known to the skilled person (see for example http://www.flexography.org). By applying an amount of hydrophobic compound in excess to what would be needed to cover the cell wall end face 34, the hydrophobic compound is allowed to spill over the end face surface 34 of the cell wall 19 and cover the end portion of the cell wall 19 including a part of the surface 21 interfacing the containment space 25.

Curing the thus formed hydrophobic end face 34 and hydrophobic surface portion 35 of the cell wall 19 results in a stable hydrophobic cap formed around the cell wall end portion. The hydrophobic cap 34, 35 allows the non-polar liquid 30 of the electrowetting optical element 1 to contact the cell wall surface 21 interfacing the containment space 25 and form a flat interface or meniscus 38 with the polar liquid 29.

An amount of spilling over of the hydrophobic compound, i.e. a length from the cell wall end face extending towards the first electrode layer stack 6, is determined by the viscosity of the hydrophobic compound and the time period in which the hydrophobic compound is allowed to spill over. The time period can be set by controlling a time between applying the hydrophobic compound to the cell wall end face and the curing of the hydrophobic compound. This time in practice can range depending on hydrophobic compound properties from a few tens of second to a few seconds.

In the flexographic printing process, the cell walls 19 can advantageously face upwards, such that gravity can cause the hydrophobic compound to spill over the edge of the cell wall end face 34 forming the hydrophobic surface portion 35 of the cell wall end portion.

Alternatively, once deposited by the flexographic printing process, adhesion of the hydrophobic compound to the surface 21 of the cell wall end portion can cause the hydrophobic compound to spill over the edge of the cell wall end face 34 forming the hydrophobic surface portion 35 of the cell wall end portion.

Cell wall 19 as a continuous barrier around containment space 25, can thus be provided circumferentially with the hydrophobic surface portion 35, i.e. at all sides. This allows the non-polar liquid 30 to be evenly distributed along the entire circumference or all sides of cell wall 19 of an electrowetting optical element 1 in unpowered state. This causes the optical density of the non-polar liquid 30 to be more uniform over the entire surface of the electrowetting optical element 1 when viewed from below or from above.

In step 304 the containment space 25 is filled with at least a polar liquid 29 and a non-polar liquid 30, the polar and non-polar liquids being immiscible with each other. First the polar liquid as described above is supplied into the containment space 25 such that the cell walls 19 do not overflow. Subsequently the non-polar liquid 30 is supplied such that the cell walls 19 overflow between adjacent electrowetting elements 1 and which are then covered with the non-polar liquid. This step can be performed with the first electrode layer stack 5 in horizontal position with the cell walls 19 in upright position.

In step 305 a second electrode layer stack 3 is provided, covering the containment space 25 having the polar and non-polar liquids 29, 30, leaving a slit 32 between the cell wall end face 34 and the second electrode layer stack 3. The second electrode layer stack 5 has a second electrode layer 13 for allowing a voltage to be applied to the first and second electrode layers 13, 6 respectively for 20 rearranging the polar liquid 29 relative to the non-polar liquid 30 as described above. Excess non-polar liquid 30 is removed sideways when the second electrode layer stack 3 is placed on top of the electrowetting optical element 1 .

The embodiments described above are intended as examples only, not to limit the scope of protection of the invention as defined in the claims below.

REFERENCE N UMERALS

1 Electrowetting optical element

2 Incident light

3 Second electrode layer stack

5 First electrode layer stack

6 First electrode layer

7 Superstrate

10 Hydrophobic interface surface

1 1 Substrate

12 Insulating layer

13 Second electrode layer

14 Reflective layer

19 Cell wall

21 Cell wall interface surface

25 Containment space

29 Polar liquid

30 Non-polar liquid

32 Slit

34 Cell wall end face

35 Hydrophobic surface portion

38 Convex meniscus shaped surface

301 Providing first electrode layer stack

302 Forming cell wall

303 Forming hydrophobic cell wall end portion

304 Filling containment space

305 Providing second electrode layer stack

Claims

1 . Electrowetting optical element (1 ) comprising

- a first electrode layer stack (5) and a second electrode layer stack (3), and

- a containment space (25) formed between said first electrode layer stack (5) and said second electrode layer stack (3);

- said containment space (25) at least containing a polar liquid (29) and a non-polar liquid (30), the polar and non-polar liquids being immiscible with each other,

- at least one cell wall (19) extending between said first and second electrode stacks (3, 5) for defining sides of said containment space (25), said cell wall (19) comprising a compound of which said cell wall (19) is composed;

- each of said second electrode layer stack (3) and said first electrode layer stack (5) comprising an electrode (13, 6) for applying a voltage to said electrodes (13,6) for allowing rearranging said polar liquid relative to said non-polar liquid;

- said at least one cell wall (19) having a surface (21 ) interfacing said containment space (25) and a hydrophobic cell wall end face (34);

- said cell wall interface surface (21 ) having a hydrophobic surface portion (35) interfacing said containment space (25) at an end portion of said cell wall (19);

characterized in

said hydrophobic surface portion (35) is arranged circumferentially around said end 20 portion of said cell wall (19).

2. Electrowetting optical element (1 ) according to claim 1 , wherein said hydrophobic surface portion (35) and said hydrophobic cell wall end surface form a continuous cap shaped hydrophobic (34, 35) surface portion around an end portion of said cell wall facing said second electrode layer (3).

3. Method of manufacturing an electrowetting optical element (1), comprising:

- providing (301 ) a first electrode layer stack (5), said first electrode layer stack (5) having a first electrode layer (6); and

- providing (302) at least one cell wall (19) extending from said first electrode stack (5) for defining sides of a containment space (25), said at least one cell wall 30 (19) having a cell wall interface surface (21) interfacing said containment space (25) and a cell wall end face (34) at an end of said cell wall (19) opposite said first electrode layer stack (5);

- filling (304) said containment space (25) with at least a polar liquid (29) and a non-polar liquid (30), said polar and non-polar liquids being immiscible with each 35 other;

- providing (305) a second electrode layer stack (3), covering said containment space (25) leaving a slit (32) between said cell wall end face (34) and said second electrode layer stack (3), said second electrode layer stack (5) having a second electrode layer (13) for allowing a voltage to be applied to said first and second electrode layers (13,6) respectively for rearranging said polar liquid (29) relative to said non-polar liquid (30);

characterized by the method further comprising:

- forming (303) a hydrophobic surface portion (35) at an end portion of said cell wall (19) interfacing said containment space (25).

4. Method according to claim 4, wherein said forming (303) a hydrophobic surface portion comprises:

- applying a hydrophobic compound to said cell wall interface surface (21 ) at an end portion of said pixel wall (19) prior to said step of filling (303) for forming a hydrophobic surface portion (35) interfacing said containment space (25) at said end portion of said cell wall (19).

5. Method of manufacturing an electrowetting optical element (1) according to claim 5, said step of applying a hydrophobic compound to said cell wall interface surface (21 ) comprising :

- applying said hydrophobic compound to said cell wall end face (34) using an excess amount of hydrophobic compound;

- allowing said excess hydrophobic compound to spill over to said surface (21 ) at said end portion (35) of said cell wall (19) such that at said end portion (35) of said cell wall (19) is covered with the hydrophobic compound, during a time period depending on de viscosity of said hydrophobic compound and a length of said end portion (35) to be covered with said hydrophobic compound; and

- curing said hydrophobic compound.