Electrowetting Optical Elements

Abstract

The present invention relates to an electrowetting optical element. The element comprises a first electrode layer stack including a substrate and a first electrode layer, a second electrode layer stack including a superstrate and a second electrode layer, a containment space formed between the first and second electrode layer stacks, and one or more cell walls extending between the first and second electrode layer stacks to define sides of the containment space forming a cell. The containment space contains a polar liquid and a non-polar liquid, the polar liquid and the non-polar liquid being immiscible with each other, and the first and second electrode layers are arranged to rearrange the polar liquid relative to the non-polar liquid upon application of a voltage between the electrodes. The first electrode layer stack further comprises an insulating layer arranged between the first electrode layer and the containment space and forming an interface with the containment space. The insulating layer comprises a first group of polymers and a second group of polymers, the first group of polymers comprising functional hydrophilic chemical groups arranged to form covalent bonds with the first electrode layer stack, and the second group of polymers comprising polymers without functional hydrophilic chemical groups, and the first group of polymers and the second group of polymers are arranged in the insulating layer as an entangled polymer network.

Description

[Technical Field]

[0001] The present disclosure relates generally to electrowetting optical elements and methods of processing electrode layer stacks in such electrowetting optical elements, and more particularly to insulating layers included in the electrode layer stacks in such electrowetting optical elements, which insulating layers improve the operational reliability of the optical elements over a wide temperature range.

[0002] Furthermore, the present disclosure relates to methods for processing such electrode layer stacks in electrowetting optical elements and in displays including such elements. [Background technology]

[0003] Electrowetting is based on altering the effective wetting preference of the hydrophobic surface of an insulating layer for non-polar liquids relative to polar liquids by varying the strength of an applied electric field across the insulating layer, whereby the insulating layer, polar liquid, and non-polar liquid become part of a capacitor assembly that also includes electrodes to which a voltage can be applied to establish an electric field across the insulating layer.

[0004] The electrowetting optical element, which may also be referred to as an electrowetting element in this disclosure in accordance with the state of the art, may be composed of a first electrode layer stack and a second electrode layer stack, respectively, from bottom to top, i.e., from the reverse viewing path. The first electrode layer stack includes at least a substrate, a first electrode layer, and an electrical insulating layer above the first electrode layer. The second electrode layer stack includes at least a superstrate and a second electrode layer.

[0005] Between the first and second electrode layer stacks, a storage space is formed in which a polar liquid and a non-polar liquid are stored between a plurality of cell walls extending between the first and second electrode layer stacks. The polar liquid and the non-polar liquid are immiscible with each other. Individual cells are formed between these cell walls and the first and second electrode layer stacks. At least one cell, preferably together with multiple cells, can define an individual pixel in an optical device in which the electrowetting optical element is disposed. A pixel is considered the smallest addressable element of a display, and therefore, in the present disclosure, a pixel element includes at least one electrowetting cell. A pixel can include any number of cells, not just one, such as an even number of cells or an odd number of cells.

[0006] The definition of "containment space" is intended to be interpreted functionally and without limitation. This means that polar or non-polar liquids may flow freely or partially from one portion of the containment space to another portion of the containment space. To allow or facilitate such movement, the cell walls disposed between the first and second electrode layer stacks do not completely enclose the polar and non-polar liquids within the containment space, but allow complete or limited movement of liquid from one cell to an adjacent cell, and thus from one portion of the containment space to an adjacent portion. Therefore, the definition of "containment space" is used as a known definition, but is not limited to the example of preventing liquid movement between adjacent containment spaces.

[0007] The above-mentioned electrowetting element is known, for example, from U.S. Pat. No. 9,274,331, which has the same assignee as the present disclosure. The electrowetting element disclosed therein is arranged to allow power supply to first and second electrode layers to relocate a polar liquid relative to a nonpolar liquid. The element has a first electrode layer stack, a second electrode layer stack, and a cell wall extending between the first and second electrode layer stacks, and typically has a configuration in which the cell wall is fixedly attached to the second electrode layer stack but non-fixedly attached to the first electrode layer stack. This non-fixed attachment can also be said to be such that an end face of the cell wall faces the first electrode layer stack so as to be in loose contact with the first electrode layer stack.

[0008] Thus, the insulating layer of the first electrode layer stack is electrically insulating to substantially prevent electrical conduction and / or short-circuiting between the first electrode layer and the polar liquid in the containment space, as described above, and may also feature a hydrophobic interface with the containment space containing the polar and non-polar liquids.

[0009] Known electrowetting displays constructed from such electrowetting optical elements have been found to degrade during high temperature operation of the display.

[0010] At room temperature, electrowetting displays can operate correctly, but when temperatures rise above room temperature or drop significantly below room temperature, the electrowetting behavior of the displays deteriorates, especially in outdoor applications. Summary of the Invention

[0011] The object of the present disclosure is to overcome the above-mentioned problems and drawbacks of the prior art, and more particularly to provide an electrowetting optical element that has an improved and more reliable electrowetting effect at temperatures significantly different from room temperature.

[0012] It is a further object of the present invention to provide a method for manufacturing or processing electrowetting optical elements that have an improved and more reliable electrowetting effect at temperatures significantly different from room temperature.

[0013] According to a first aspect of the present disclosure, the above-mentioned object is achieved by an electrowetting optical element, the electrowetting optical element comprising: a first electrode layer stack including a substrate and a first electrode layer; a second electrode layer stack including a superstrate and a second electrode layer; an accommodation space formed between the first electrode layer stack and the second electrode layer stack; one or more cell walls extending between the first electrode layer stack and the second electrode stack to define sides of the containment space forming a cell; Equipped with The containing space contains a polar liquid and a non-polar liquid, and the polar liquid and the non-polar liquid are immiscible with each other; the first electrode layer and the second electrode layer are arranged to apply a voltage between the electrodes to relocate the polar liquid relative to the non-polar liquid; The first electrode layer stack further includes an insulating layer disposed between the first electrode layer and the accommodating space and forming an interface with the accommodating space, the insulating layer including a first group of polymers and a second group of polymers, the first group of polymers including functional hydrophilic chemical groups arranged to form covalent bonds with the first electrode layer stack, the second group of polymers including polymers without functional hydrophilic chemical groups, and the first group of polymers and the second group of polymers arranged in the insulating layer as an entangled polymer network.

[0014] The operating principle of an electrowetting device is as follows. In the unpowered state or power-off mode of the first and second electrodes, i.e., when no voltage is applied between the first and second electrodes, the system is in its lowest energy state when the nonpolar liquid forms a boundary layer between the polar liquid and the hydrophobic surface of the insulating layer. This occurs because the nonpolar liquid preferentially wets the hydrophobic surface, effectively repelling the polar liquid from contact with the hydrophobic surface. If the nonpolar liquid is optically absorbing over at least a portion of the visible wavelength range, the optical absorption of the nonpolar liquid creates an obstacle to incident light passing through the system, thereby creating an electrowetting device with reduced optical transmittance over at least a portion of the visible wavelength range. When a voltage is applied between the first and second electrodes, an electric field is established between the second electrode (which is short-circuited with the conductive polar liquid) and the first electrode across the combined thickness of the insulating layer and the nonpolar liquid. The lowest energy state of the system is when the nonpolar liquid, which is less conductive or insulating, is at least partially displaced by the conductive polar liquid due to the force of the applied electric field. In effect, applying a voltage between the electrodes reduces the preferential wetting of the hydrophobic surface by the nonpolar liquid. If the applied voltage is large enough, the hydrophobic surface becomes preferentially wetted by the polar liquid, thereby displacing the nonpolar liquid from the hydrophobic surface. Within the electrowetting cell, the shape of the displaced nonpolar liquid changes from a lenticular liquid film to a contracted droplet. In this case, if the polar liquid is substantially optically non-absorbing in the visible wavelength range, incident light passing through the system is less subject to optical absorption by the nonpolar liquid, thereby improving the optical transmission of the incident light through the electrowetting element.

[0015] Switching the electrodes from a powered to a non-powered state neutralizes the electric field across the insulating layer by removing the voltage applied between the electrodes, and the system returns to the lowest energy state of the system that existed before the electrodes were powered, with the hydrophobic layer being preferentially wetted by the non-polar liquid in the form of a non-polar liquid film, thereby displacing the polar liquid from the hydrophobic surface of the insulating layer.

[0016] We found that the physical and chemical properties of the insulating layer play an important role in realizing an electrowetting device that can maintain the structural integrity of the insulating layer and its high hydrophobicity during electrowetting operation over a wide temperature range from approximately -30°C to 70°C.

[0017] Prior art insulating layers comprising primarily inorganic materials are notorious for having defects and pinholes in the inorganic portion of the insulating layer, which easily result in conduction current and / or short circuits during electrowetting operation when a potential difference is applied across the insulating layer.

[0018] Prior art hydrophobic hydrocarbon or fluorocarbon monolayers placed on insulating organic or inorganic layers have been found to rapidly suffer chemical degradation during electrowetting operation, especially at high temperatures (outdoors). Chemical degradation at the interface between the insulating layer and the polar liquid tends to make the interface more hydrophilic, impairing electrowetting behavior in response to an applied potential difference across the insulating layer. Thus, it is essential that the interface be able to maintain high hydrophobicity over a wide temperature range during electrowetting operation.

[0019] The insulating layer used in known devices may comprise only a single thick layer of a fluorocarbon material such as Teflon AF (DuPont), Cytop-S (AGC Chemicals), Fluoropel (Cytonix), etc. Such insulating layers are known to have poor adhesion to the electrode materials and are further known to suffer from pinholes and defects.

[0020] It has been found that insulating layers composed of these fluorocarbon material layers generally lack functional chemical groups that can bond with electrode materials, for example, functional chemical groups that form covalent bonds with hydroxyl groups on the electrode (ITO) surface and / or the glass substrate surface, and therefore may have problems with adhesion to the electrode material, resulting in peeling.

[0021] Cytop-M (AGC Chemicals) is a well-known insulating polymer material that can be bonded to electrodes and / or glass surfaces. Cytop-M has functional aminosilane groups at both ends of the polymer chain for chemical bonding with hydroxyl groups on electrodes (ITO) and / or glass surfaces. However, it has been shown that the insulating layer of Cytop-M material gradually loses its hydrophobicity when exposed to polar liquids, especially at high temperatures. This loss of hydrophobicity is attributed to the migration of unbound hydrophilic aminosilane end groups on the fluorocarbon chains of the polymer to the interface between the insulating layer and the polar liquid. Furthermore, it has been well-known that fluorocarbon layers made of Cytop-M have numerous defects that cause rapid electrical breakdown when used as insulating layers.

[0022] However, an insulating layer comprising a chemically crosslinked hydrocarbon material covalently bonded to an ITO electrode material or another inorganic insulating material layer disposed on the ITO electrode material can also be achieved using parylene. Parylene initially exhibits the desired electrowetting behavior in a polar liquid environment, but the parylene / polar liquid interface gradually becomes less hydrophobic, likely due to hydrolysis of the parylene material, resulting in the formation of oxygen-containing hydrophilic chemical groups at the interface. Polar liquids typically include polar liquids such as water, ethylene glycol, and / or glycerol, or mixtures thereof. Nonpolar liquids typically consist of alkane liquids such as decane and dodecane.

[0023] An electrowetting optical element according to the present disclosure comprises a first electrode layer stack and a parallel second electrode layer stack spaced apart from each other. The distance between the first and second electrode layer stacks is spanned by a plurality of cell walls that form separate spaces between the two stacks. These spaces, sometimes called cells, may be embodied as completely sealed containment spaces containing immiscible polar and non-polar liquids. Alternatively, the spaces may be containment spaces in which one of the liquids, e.g., the polar liquid, is only loosely contained, allowing some migration of the liquid into an adjacent space. For example, the containment space may be configured such that the cell wall is fixedly attached to one of the electrode layer stacks and is only in loose mechanical contact with the opposing electrode layer stack, allowing a small amount of non-polar liquid to migrate into the adjacent cell or containment space. The present disclosure is not limited to any one of these configurations and may be embodied in any configuration of an electrowetting element in which the first electrode layer stack includes at least a substrate and an insulating layer.

[0024] The first electrode layer stack includes an insulating layer disposed on top of the stack and in contact with the containment space and, therefore, the polar and non-polar liquids contained in the space.

[0025] It was the inventors' insight that an insulating layer comprising two polymers with different properties could combine the best of two worlds, such that on the one hand it is possible to achieve a strong bond with the first electrode layer stack, e.g. the ITO material of the electrode layer and / or the glass substrate, and on the other hand it is possible to maintain a high degree of hydrophobicity at the interface with polar and non-polar liquids.

[0026] The insulating layer comprises a first group of polymers and a second group of polymers, the first group of polymers being arranged to form covalent bonds with the first electrode layer stack and therefore comprising functional hydrophilic chemical groups capable of bonding with the first electrode layer stack, and the second group of polymers comprising polymers that do not have functional hydrophilic chemical groups, and the second group of polymers having no hydrophilic chemical groups, so that even when the polymers migrate across the insulating layer to an interface with a polar liquid, the hydrophobicity of the interface is maintained and degradation is prevented.

[0027] The formation of an entangled polymer network between the first group of polymers and the second group of polymers results in a strong mechanical bond between the two groups of polymers: the first group already features strong chemical (covalent) bonds with the first electrode layer stack, and has sufficiently long polymer chain lengths to allow the second group of polymers to entangle with the first group of polymers, resulting in an entangled polymer network.

[0028] Entanglement can be defined as intermolecular chain entanglement, and thus, although there may be a level of entanglement between chains of polymers of the same group, especially those having long polymer chain lengths, the polymers of the first group and the polymers of the second group are linked by intermolecular chain entanglement in accordance with the present disclosure.

[0029] Entanglement can be achieved or facilitated by the presence of dangling loops in the polymer chains of the first group of polymers, where the loops are formed between two functional groups on the chains that are covalently bonded to the first electrode layer stack. The loops between the bonded functional groups provide space for the chains of the second group of polymers to pass through the loops during deposition, resulting in a degree of entanglement. The dimensions of the loops depend on various aspects, including the number of functional hydrophilic chemical groups per unit chain length, the polymer chain length, and the free volume of the polymer matrix created by the voids left between the entangled polymer chains. Therefore, the effective free volume or average size of the loops can be determined by the average distance between two adjacent covalent bonds that bond a single polymer chain of the first group of polymers to the first electrode layer stack, as well as the free volume that can exist between multiple polymer chains of the first group that share several covalent bonds with the first electrode layer stack. Thus, entanglement can be interpreted as polymer entanglement of the second group of polymers through loops of polymer chains of the first group of polymers on the surface of the first electrode stack, or polymer entanglement of the second group of polymers through free volume present between multiple polymer chains of the first group of polymers.

[0030] The first group of polymers is deposited at a level or height in such a way as to provide sufficient loops or free volume for the second group of polymers to intertwine during and after deposition. Preferably, the first group of polymers is deposited as a polymer monolayer, characterized in that all of the deposited polymer chains are covalently bonded to the first electrode layer stack. Polymers from the second group of polymers are then deposited as a multilayer, or at least in a volume or amount such that the deposited second group of polymers overlay the deposited polymers from the first group, achieving a deposition thickness that substantially exceeds the thickness of the deposited first group of polymers. Preferably, the volume of the second group of polymers disposed on the deposited first group of polymers is such that a thickness is achieved that at least substantially corresponds to, but preferably exceeds, the extended chain length of the deposited polymers from the first group. This has the effect that even if any of the deposited polymer chains of the first group extends from the covalent bond site attached to one end of the polymer chain towards the interface with the containment space, the opposite end of the polymer chain will not be able to reach the surface of the insulating layer and thus the interface with the polar liquid due to its limited chain length, and thus the deposited polymers of the second group cover the deposited polymers of the first group in such a way that they are substantially hidden and buried.

[0031] Thus, the insulating layer can be considered to comprise a laminated fluorocarbon layer having two sub-layers, the first layer being included in the support layer or electrode layer stack and comprising a first polymeric fluorocarbon having functional chemical groups positioned to form covalent bonds with the attached hydroxyl groups, and the second layer being above the first layer and comprising a second polymeric fluorocarbon preferably comprising only fluorocarbon moieties.

[0032] Preferably, the insulating layer is capable of adhering or bonding to a support layer included in the first electrode layer stack, the support layer comprising: Electrode materials on the substrate surface, ·Inorganic nonmetallic materials, Organic materials, preferably chemically crosslinked organic materials Here, the material forming the support layer other than the electrode material itself is ionically or covalently bonded to the electrode material on the substrate surface. When the electrode material on the substrate surface is present as a patterned electrode material on glass, the support layer is also ionically or covalently bonded to the glass.

[0033] In one example, the first group of polymers and the second group of polymers have polymer chains that include at least 100 monomers, preferably at least 250 monomers, and more preferably at least 500 monomers.

[0034] In one example, the first group of polymers and the second group of polymers have polymer chain lengths of at least 100 nm, preferably at least 200 nm, more preferably at least 250 nm.

[0035] Several (intrinsic) properties of the polymer may influence, determine, or promote the level of entanglement between the two groups of deposited polymers. These properties are believed to be related to the chain length of the polymer. The longer the polymer chain, the more free volume and loops there are, which promotes chain entanglement. The number of covalent bonds per polymer, defined by the number of functional chemical groups per polymer chain, may determine the degree to which the two groups of polymers tend to entangle. Therefore, the level of entanglement can be controlled or determined by selecting one or more of the polymer chain length, the number of functional chemical groups per polymer chain, and therefore the free volume in the deposited composite polymer layer, and the size of the dangling loops of the first group of polymers deposited during the deposition of the second group of polymers.

[0036] In one example, the deposited polymer from the first group of polymers is characterized as being present as a monolayer of polymer, with all of the polymers in the monolayer being covalently bonded to the first electrode layer stack.

[0037] In one example, the deposited polymer from the second group of polymers is present as multiple layers of polymer.

[0038] Preferably, the thickness of the deposited polymer layer from the first group of polymers is thinner than the thickness of the deposited polymer layer from the second group of polymers. More specifically, the first group of polymers can be deposited substantially as a monolayer, while the second group of polymers can be deposited as a thicker multilayer. At the interface between the monolayer and the multilayer, the deposited first group of polymers and second group of polymers exist as an entangled matrix.

[0039] In one example, the deposited entangled polymer network includes a monolayer of a first group of polymers covalently bonded to functional chemical groups on the first electrode layer stack and multiple layers of a second group of polymers entangled with the first group of polymers via dangling polymer chain loops of the first group of polymers, both ends of which are bonded to functional chemical groups on the first electrode layer stack.

[0040] In one example, the second group of polymers includes polymers that include hydrophobic chemical moieties.

[0041] In one example, the first group of polymers includes polymers included in the first electrode layer stack that have a single functional chemical end group positioned to form a covalent bond with a hydroxyl group attached to the first electrode layer stack.

[0042] In one example, the first group of polymers includes two monofunctional end groups positioned to form covalent bonds with hydroxyl groups included in the first electrode layer stack and attached to the first electrode layer stack.

[0043] The first group of polymers has at least one, and preferably multiple, functional chemical groups on each polymer chain, and polymers having multiple such functional chemical groups arranged to form covalent bonds with hydroxyl groups on the first electrode layer stack have the effect of promoting stronger bonding of the deposited first group of polymers to the first electrode layer stack compared to polymers having only one such functional chemical group.

[0044] In one example, the first electrode layer stack further includes a support layer disposed between the first electrode layer and the insulating layer and including one or more materials selected from the group consisting of inorganic non-metallic materials having high electrical resistivity and organic materials, more preferably chemically cross-linked organic materials having high electrical resistivity.

[0045] The insulating layer may also be bonded (covalently bonded) to the stack via a support layer, preferably made of an organic or inorganic non-metallic material.

[0046] In one example, the support layer comprises an organic parylene, preferably an organic parylene contained in the first electrode layer and covalently bonded to hydroxyl groups attached to the first electrode layer, preferably via a silane adhesion promoter.

[0047] In one example, the parylene is parylene-C, more preferably parylene-N, and most preferably parylene-HT.

[0048] Although parylene initially enables the desired electrowetting behavior in polar liquid environments, the parylene / polar liquid interface gradually becomes less hydrophobic, likely due to hydrolysis of the parylene material, which generates oxygen-containing hydrophilic chemical groups at the interface and degrades the hydrophobicity of this interface upon exposure to polar and non-polar liquids.

[0049] Support layers embodied as inorganic multilayer stacks are known to have much fewer defects than single inorganic layers, but the deposition process is costly and impractical, and inorganic multilayer stacks require a topcoat of a fluorocarbon material to prevent the fluorocarbon material from suffering from the aforementioned problems of fluorocarbons sooner or later impairing the electrowetting behavior.

[0050] In one example, one or both of the first group of polymers and the second group of polymers comprises a fluoropolymer, which has at least one or more properties of optical transparency, electrical insulation, high hydrophobicity, and high chemical resistance.

[0051] In one example, the first group of polymers consists of Cytop-M.

[0052] In one example, the second group of polymers consists solely of fluorocarbon moieties.

[0053] In one example, the second group of polymers consists of Cytop-S.

[0054] In a further aspect, the present disclosure provides a method of processing an electrode layer stack for the manufacture of an electrowetting optical element, the method comprising: providing an electrode layer stack comprising a substrate and an electrode layer; providing an insulating layer on the electrode layer stack to form an interface with a receiving space within the electrowetting optical element; Equipped with The insulating layer is formed by the following successive steps: depositing a first group of polymers onto the electrode layer stack; removing the first group of polymers that are not covalently bonded to the electrode layer stack; Depositing a second group of polymers onto the electrode layer stack the first group of polymers and the second group of polymers are formed to be entangled as a polymer network in the insulating layer; The first group of polymers comprises at least one functional hydrophilic chemical group included in the electrode layer stack and positioned to form a covalent bond with a hydroxyl group attached to the electrode layer stack, and the second group of polymers comprises polymers that do not have a functional hydrophilic chemical group.

[0055] In one example, the first group of polymers and the second group of polymers are deposited by wet chemical dip coating from corresponding polymer solutions.

[0056] In one example, a portion of the first group polymer is removed by immersing the electrode layer stack in a fluorocarbon solvent configured to dissolve the first group polymer to dissolve and remove the first group polymer that is not covalently bonded to the hydroxyl groups included in and attached to the electrode layer stack.

[0057] In one example, the method includes, between the step of depositing the first group of polymers and the step of removing a portion of the first group of polymers, Annealing the electrode layer stack including the first group of polymers wherein the annealing step is carried out at a high temperature, preferably above 100°C.

[0058] In one example, the method includes, prior to the step of providing the insulating layer: Chemically activating the first electrode layer to allow covalent bonding with the first group of polymers. Further provided with:

[0059] In one example, the method comprises, before the step of providing an insulating layer, the following successive steps: providing a support layer on the first electrode layer; chemically activating the surface of the support layer to allow covalent bonding with the first group of polymers in the insulating layer; The support layer comprises one or more materials selected from the group consisting of inorganic non-metallic materials and organic materials having high electrical resistivity, more preferably chemically crosslinked organic materials having high electrical resistivity.

[0060] In one example, the chemically activating step is performed by adding hydroxyl groups.

[0061] In one example, the support layer is an organic parylene layer that is covalently bonded to hydroxyl groups on the ITO material of the substrate electrode by the Silane A-174 adhesion promoter during parylene deposition. Chemical activation, which hydrophilizes the substrate electrode, allows a higher density of Silane A-174 molecules to be covalently bonded to the electrode material, thereby improving adhesion between the parylene layer and the substrate electrode. The parylene layer is activated after deposition by selective UV-O3 or oxygen plasma treatment to control the density of hydroxyl groups on the surface. These hydroxyl groups can form covalent bonds with reactive silane groups attached to the backbone of the first polymeric fluorocarbon material when the first polymeric fluorocarbon material is deposited (e.g., by dip coating) on ​​the activated parylene layer and then annealed at T > 100°C, preferably in an oxygen-free environment. Any fluorocarbon material not covalently bonded to the parylene is then removed by immersing the substrate in a fluorocarbon solvent capable of dissolving the first polymeric fluorocarbon material. Subsequently, after removing the solvent by evaporation, only the covalently bonded fluorocarbon material remains on the parylene layer. Annealing the first fluorocarbon sublayer at a temperature T > 100°C effectively forms a first fluorocarbon sublayer comprising a polymeric fluorocarbon monolayer lying flat on the parylene surface. A second fluorocarbon sublayer is then cast onto the first fluorocarbon sublayer, preferably characterized by the same fluorocarbon material as the first fluorocarbon material, except that it lacks reactive silane or other hydrophilic chemical groups. During deposition of the second fluorocarbon material from the fluorocarbon solvent, the first polymeric fluorocarbon material again surrounds itself with solvent molecules and partially exfoliates from the support surface, forming a dangling loop between the two covalently bonded sites on its backbone. This allows the second polymeric fluorocarbon material to become entangled with the first polymeric fluorocarbon material during deposition in the presence of a fluorocarbon solvent, and then the entanglement hardens upon removal of the solvent during a second anneal of the entangled polymer network at T > 100°C, the second anneal preferably being performed in an inert, oxygen-free environment.The second fluorocarbon sublayer is substantially thicker than the first fluorocarbon sublayer, preventing unreacted functional groups on the first polymeric fluorocarbon material from being exposed at the interface between the polar liquid and the composite fluorocarbon layer in an electrowetting display. This results in a composite fluorocarbon layer that is firmly anchored to the support layer while maintaining a hydrophobic interface with the polar liquid. The support layer is firmly anchored to the substrate electrode material.

[0062] In one example, a method of processing an electrode layer stack for manufacturing an electrowetting optical element comprises: providing an electrode layer stack comprising a substrate and an electrode layer; providing cell walls on the electrode layer stack, the cell walls extending from the electrode layer stack and defining a surface of a three-dimensional non-planar shape so as to at least partially define a containment space enclosing the polar liquid and the non-polar liquid; providing an insulating layer on the electrode layer stack, on the electrode layers and on the cell walls, so as to form an interface with the containment space; Equipped with The insulating layer is formed by the following successive steps: depositing a first group of polymers onto the electrode layer stack; removing the first group of polymers that are not covalently bonded to the electrode layer stack; Depositing a second group of polymers onto the electrode layer stack the first group of polymers and the second group of polymers are formed to be entangled as a polymer network in the insulating layer; The first group of polymers comprises at least one functional hydrophilic chemical group included in the electrode layer stack and positioned to form a covalent bond with a hydroxyl group attached to the electrode layer stack, and the second group of polymers comprises polymers that do not have a functional hydrophilic chemical group.

[0063] The insulating interface layer according to the present disclosure, formed by depositing two groups of polymers, e.g., Cytop-M and Cyto-S, may be formed on a flat, planar, two-dimensional surface of the electrode layer, but according to the above example, may also be formed on a non-flat, non-planar, three-dimensional surface. When cell walls are provided on the electrode layer, the planar surface of the electrode layer becomes an embossed surface with raised cell walls and recessed cells that define containment spaces in which polar and non-polar liquids are enclosed.

[0064] The insulating interface layer according to the present disclosure formed by depositing two polymer groups, e.g., Cytop-M and Cytop-S, may alternatively be disposed on a support layer formed by one or more materials from the group comprising inorganic non-metallic materials and organic materials, preferably chemically cross-linked organic materials, which are ionically or covalently bonded to the electrode layer material and, if a cell wall is provided on the electrode layer, to the cell wall material.

[0065] In yet another aspect of the present disclosure, there is provided an electrowetting optical display including one or more electrowetting optical elements according to any of the previous aspects or examples thereof.

[0066] Each example described in relation to the first aspect of the invention may also be applied in relation to the second or other aspects of the invention, and correspondingly, all advantages of the first aspect and its further examples also apply to the second or other aspects and examples thereof or examples of the first aspect.

[0067] The present invention will now be further described with reference to the accompanying drawings, in which embodiments of the invention are shown. [Brief explanation of the drawings]

[0068] [Figure 1] 1 shows an exemplary electrode layer stack of an electrowetting element according to the prior art; [Figure 2] 1 is an exemplary diagram illustrating an electrode layer stack of an electrowetting element according to the present disclosure. [Figure 3] 3A-3C are diagrams illustrating several steps in processing an electrode layer stack of an electrowetting element according to the present disclosure. [Figure 4] 1A to 1C are diagrams illustrating exemplary embodiments of electrode layer stacks of electrowetting elements according to the present disclosure. [Figure 5] 1A to 1C are diagrams illustrating exemplary embodiments of electrode layer stacks of electrowetting elements according to the present disclosure. [Figure 6] 1A to 1C are diagrams illustrating exemplary embodiments of electrode layer stacks of electrowetting elements according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0069] Figure 1 shows details of an electrowetting optical element in the art. An electrowetting display (EWD) comprises an electrowetting optical element including a transparent substrate, a transparent superstrate substrate arranged parallel to the substrate, and a liquid layer sandwiched between the two substrates. Both substrates are provided with electrodes facing the liquid layer, which includes a transparent polar liquid layer and a colored non-polar liquid that is immiscible with the polar liquid. The substrates further comprise an insulating layer disposed on the substrate electrodes.

[0070] As shown in Figure 1, the insulating layer 102 separates the polar liquid in electrical short-circuit contact with the superstrate electrode from the substrate electrode layer 103, or the support layer 103 on the substrate electrode layer. When the substrate electrode and superstrate electrode are at different potentials, a potential difference is created across the insulating layer 102. The material and thickness of the insulating layer are selected to minimize the possibility of problems such as electrical breakdown and / or leakage current across the insulating layer at the maximum applied potential drop. These problems are typically due to defects in the insulating layer.

[0071] The non-polar liquid 106 is a colored oil that resides at the interface between the insulating layer 102 and the polar liquid layer. In the present device, it is desirable for the oil to spread completely across the interface between the insulating layer 102 and the polar liquid layer (i.e., completely wet with a contact angle of substantially zero) when there is zero potential drop across the insulating layer. This is made possible by rendering the insulating layer surface exposed to the polar liquid hydrophobic.

[0072] When a potential difference is established across the insulating layer by applying different potentials to the substrate and superstrate electrodes, the oil layer on the insulating layer breaks up into droplets, and the droplets assume a non-zero contact angle (i.e., partial wetting) on ​​the insulating layer in a polar liquid environment, with the contact angle increasing with increasing potential difference. This is known as the electrowetting effect, a key aspect of EWD operation and has been widely documented in the literature. When the oil on the insulating layer is partially wetted, the EWD becomes partially transparent; when the oil is fully wetted, the EWD becomes opaque to an extent determined by the color of the oil and the thickness of the oil layer.

[0073] Prior art electrowetting devices can include an insulating layer composed entirely of hydrocarbon materials, entirely of fluorocarbon materials, or composed of at least two different materials. In the latter case, insulating layers have been described that include an organic or inorganic support layer in contact with the substrate electrode and a hydrophobic organic top layer in contact with the oil and polar liquid. The hydrophobic top layer can be a silane-type hydrocarbon or fluorocarbon monolayer, or a thick hydrocarbon or fluorocarbon layer deposited by a coating process.

[0074] Figure 1 shows details of such a prior art electrowetting element, particularly the configuration of the insulating layer 102. The insulating layer 102 in Figure 1 is composed of fluorocarbon polymers 104a-d having chemical functional (terminal) groups (shown as open circles) that can form covalent bonds with hydroxyl groups on a layer below the insulating layer 102, such as a glass substrate layer or an ITO electrode layer 103 or a support layer 103 disposed on the ITO electrode layer. As can be seen in Figure 1, some of the polymers 104a, 104b form such covalent bonds with layer 103, while other polymers 104c, 104d do not.

[0075] When the insulating layer 102 is composed of only a single fluorocarbon material, such as Cytop-M (AGC Chemicals), it contains functional silane groups for chemical bonding to ITO or glass. However, it is observed that the layer gradually loses its hydrophobicity upon exposure to polar liquids, especially at high temperatures. This is illustrated in Figure 1, where some of the polymers 104c and 104d in the insulating layer 102 migrate to the surface, reducing the hydrophobicity of the polymeric fluorocarbon surface as hydrophilic, unreactive functional silane groups come into contact with polar liquids. Furthermore, fluorocarbon layers are known to have numerous defects that cause rapid electrical breakdown when used as insulating layers. As a result, structural integrity and hydrophobicity cannot be maintained, resulting in a reduced electrowetting effect.

[0076] FIG. 2 illustrates an example of an electrowetting element 200 according to one embodiment of the present disclosure. The insulating layer of the element 200 illustrated in FIG. 2 includes a transparent layer of substrate electrode material that can be chemically activated to provide a high surface density of hydroxyl groups to induce a high degree of surface hydrophilicity. A chemically activated support layer 203 can be provided on top of the electrode layer. The activation of the chemically activated support layer 203 results in hydroxyl groups on its surface that point away from the substrate electrode. An insulating layer 202 is provided on top of the support layer 203. The insulating layer 202 includes a composite fluorocarbon layer on the activated support layer 203 that has a blend of two groups of polymers. The first group of polymers is formed by polymeric fluorocarbon materials that can form covalent bonds with hydroxyl groups on the support layer via a single functional chemical end group attached to each polymer chain. These are designated polymers 204a and 204b. The second group of polymers formed on the first group comprises a second polymer material that contains only fluorocarbon moieties 205a, 205b and therefore cannot form covalent bonds with hydroxyl groups on the support layer 203.

[0077] The first and second groups are capable of intermixing with each other, thereby forming an entangled polymer network 204, 205, thereby forming strong adhesive contact between the fluorocarbon sub-layers, with the first group of fluorocarbon materials present as a polymer monolayer with functional chemical groups capable of forming covalent chemical bonds with hydroxyl groups on the surface of the support layer, and the second group of fluorocarbon materials present as a polymer multilayer without functional or other hydrophilic chemical groups.

[0078] The insulating layer may be formed directly on the electrode layer, for example an ITO electrode, but may also be formed on a support layer formed of one or more materials from the group including inorganic non-metallic materials, organic materials, preferably chemically cross-linked organic materials.

[0079] The materials forming the support layer, other than the electrode material itself, are ionically or covalently bonded to the electrode material on the substrate surface. If the electrodes on the substrate surface are present as patterned electrodes on glass, the support layer is also ionically or covalently bonded to the glass.

[0080] 3a-3c illustrate the processing of an electrode layer stack, in particular the formation of an insulating layer on an electrode layer stack for an electrowetting optical element, in accordance with the present disclosure.

[0081] In a first step, an electrode layer stack is provided, including a substrate and an electrode layer, on which an insulating layer is provided to form an interface with the containment space, which is not yet formed in this processing step, but in which air 307 is initially present.

[0082] The insulating layer is formed by first depositing a first group of polymers, e.g., by dip coating. Hydroxyl groups on a support layer 303, e.g., parylene, can form covalent bonds 304a, 304b with reactive silane groups attached to the backbone of the first group of polymers, e.g., a first polymeric fluorocarbon material, upon deposition on the activated parylene layer and subsequent first annealing at T > 100°C, preferably in an oxygen-free environment.

[0083] All fluorocarbon material not covalently bonded to the parylene is then removed, as shown in Figure 3b. This can be accomplished by immersing the substrate 320 in a fluorocarbon solvent capable of dissolving the first polymeric fluorocarbon material. Only the covalently bonded fluorocarbon material 304a, 304b is then left on the parylene layer 303, effectively forming a first group of polymer or fluorocarbon sublayers comprising a polymeric fluorocarbon monolayer lying flat on the parylene surface after a first anneal at a temperature T > 100°C to remove the solvent.

[0084] A second group of fluorocarbon polymers 305a, 305b, which form a second fluorocarbon sub-layer, is then cast onto the first group of fluorocarbon polymers 304a, 304b. Preferably, the second group is characterized by the same fluorocarbon material as the first fluorocarbon material, except that it does not have reactive silane or other hydrophilic groups, as indicated by the absence of circles on the polymers of the second group 305a, 305b.

[0085] Upon deposition of the second group of fluorocarbon materials from the fluorocarbon solvent, the first polymeric fluorocarbon material surrounds itself with solvent molecules and partially exfoliates from the substrate surface, forming dangling loops between adjacent covalently bonded sites on its backbone. This allows the second polymeric fluorocarbon material to easily entangle with the first polymeric fluorocarbon material in the presence of the fluorocarbon solvent. This entanglement is then fixed or cured upon removal of the solvent during a second anneal at T > 100°C, preferably performed in an inert, oxygen-free environment, thereby producing an electrowetting optical element, more specifically, a first electrode layer stack for an electrowetting optical element with improved properties, as shown in Figure 3c, having a strong covalently bonded reactive silane group at the bottom of the stack and no reactive silane or other hydrophilic groups at the top of the stack, with the insulating layer maintaining its structural integrity through both groups of entangled polymers.

[0086] 4, 5 and 6 show some embodiments of the first electrode layer stack of an electrowetting element according to the present disclosure.

[0087] 4, insulating layers 440, 450 are disposed on top of a parylene layer 430 and on top of a chemically activated hydrophilic ITO electrode 420 on a glass substrate 410. The insulating layers 440, 450 comprise composite fluorocarbon layers including a first sub-layer 440 of a first polymeric fluorocarbon material and a second sub-layer 450 of a second polymeric fluorocarbon material.

[0088] 5, insulating layers 540, 550 are disposed on a chemically activated hydrophilic ITO electrode 520 on a glass substrate 510. The insulating layers 540, 550 comprise composite fluorocarbon layers including a first sub-layer 540 of a first polymeric fluorocarbon material and a second sub-layer 550 of a second polymeric fluorocarbon material.

[0089] 6 shows an example using an insulating support layer 635. The support layer 635 is disposed on a chemically activated hydrophilic ITO electrode 620 on a glass substrate 610. Insulating layers 640, 650 are disposed on the chemically activated support layer 635, and the insulating layers 640, 650 include a first sublayer 640 of a first polymeric fluorocarbon material and a second sublayer 650 of a second polymeric fluorocarbon material, similar to the other examples shown in FIGS. 4 and 5. The support layer 635 itself may also be a composite support layer including an insulating inorganic sublayer and an insulating organic sublayer.

[0090] As those skilled in the art will recognize, the present invention can be practiced other than as specifically described herein. Obvious modifications to the disclosed embodiments, and specific design choices, will be apparent to those of ordinary skill in the art. The scope of the present invention is defined solely by the appended claims.

Claims

1. a first electrode layer stack including a substrate and a first electrode layer; a second electrode layer stack including a superstrate and a second electrode layer; an accommodating space formed between the first electrode layer stack and the second electrode layer stack; one or more cell walls extending between the first electrode layer stack and the second electrode layer stack to define sides of the containment space forming a cell; Equipped with the containing space contains a polar liquid and a non-polar liquid, the polar liquid and the non-polar liquid are immiscible with each other; the first electrode layer and the second electrode layer are arranged to apply a voltage between the electrodes to relocate the polar liquid relative to the non-polar liquid; The first electrode layer stack further includes an insulating layer disposed between the first electrode layer and the accommodating space and forming an interface with the accommodating space, the insulating layer including a first group of polymers and a second group of polymers, the first group of polymers including functional hydrophilic chemical groups disposed to form covalent bonds with the first electrode layer stack, the second group of polymers including polymers without functional hydrophilic chemical groups, and the first group of polymers and the second group of polymers being disposed in the insulating layer as an entangled polymer network.

2. 2. The electrowetting optical element according to claim 1, wherein the first group of polymers and the second group of polymers have polymer chains comprising at least 100 monomers, preferably at least 250 monomers, more preferably at least 500 monomers.

3. 3. An electrowetting optical element according to claim 1 or 2, wherein the first group of polymers and the second group of polymers have polymer chain lengths of at least 100 nm, preferably at least 200 nm, more preferably at least 250 nm.

4. An electrowetting optical element according to any one of claims 1 to 3, wherein the first group of polymers is a monolayer of polymers and at least substantially all, preferably all, of the polymers in the monolayer of polymers are covalently bonded to the first electrode layer stack.

5. 5. The electrowetting optical element according to any one of claims 1 to 4, wherein the second group of polymers is a multilayer of polymers.

6. 6. An electrowetting optical element according to any one of claims 1 to 5, wherein the entangled polymer network comprises a single layer of the first group polymer covalently attached to the first electrode layer stack and multiple layers of the second group polymer entangled with the first group polymer via a dangling polymer chain loop formed between two functional chemical groups on a polymer chain from the first group polymer, both of which are covalently bonded to the first electrode layer stack.

7. 7. The electrowetting optical element according to any one of claims 1 to 6, wherein the second group of polymers comprises polymers consisting of hydrophobic chemical moieties.

8. 8. An electrowetting optical element according to any one of claims 1 to 7, wherein the first group of polymers comprises polymers having a single functional chemical end group that is included in the first electrode layer stack and that is positioned to form a covalent bond with a hydroxyl group attached to the first electrode layer stack.

9. An electrowetting optical element according to any one of claims 1 to 8, wherein the first group of polymers comprises two functional end groups arranged to form covalent bonds with hydroxyl groups contained in the first electrode layer stack and attached to the first electrode layer stack.

10. The electrowetting optical element of any one of claims 1 to 9, wherein the first electrode layer stack further comprises a support layer disposed between the first electrode layer and the insulating layer and comprising one or more materials selected from the group consisting of inorganic non-metallic materials having high electrical resistivity and organic materials, more preferably chemically cross-linked organic materials having high electrical resistivity.

11. 11. The electrowetting optical element of claim 10, wherein the support layer comprises an organic parylene, preferably contained in the first electrode layer and covalently bonded to hydroxyl groups attached to the first electrode layer, or contained in an inorganic non-metallic layer disposed between the first electrode layer and the organic parylene layer and covalently bonded to hydroxyl groups attached to the inorganic non-metallic layer, the covalent bond preferably being via a silane adhesion promoter.

12. 12. The electrowetting optical element according to claim 11, wherein said organic parylene is parylene-C, more preferably parylene-N, most preferably parylene-HT.

13. 13. An electrowetting optical element according to any one of claims 1 to 12, wherein one or both of the first group of polymers and the second group of polymers comprises a fluoropolymer, and the fluoropolymer has at least one or more properties of optical transparency, electrical insulation, high hydrophobicity, and high chemical resistance.

14. 14. The electrowetting optical element according to any one of claims 1 to 13, wherein the first group of polymers consists of Cytop-M.

15. 15. The electrowetting optical element according to any one of claims 1 to 14, wherein the second group of polymers consists solely of fluorocarbon moieties.

16. 16. The electrowetting optical element according to any one of claims 1 to 15, wherein the second group of polymers consists of Cytop-S.

17. 1. A method of processing an electrode layer stack for manufacturing an electrowetting optical element, comprising: providing an electrode layer stack comprising a substrate and an electrode layer; providing an insulating layer on the electrode layer stack to form an interface with a receiving space within the electrowetting optical element; Equipped with The insulating layer is depositing a first group of polymers onto the electrode layer stack; removing the first group of polymers that are not covalently bonded to the electrode layer stack; depositing a second group of polymers onto the electrode layer stack; the first group of polymers and the second group of polymers are formed to be entangled as a polymer network in the insulating layer; A method of processing an electrode layer stack for manufacturing an electrowetting optical element, wherein the first group of polymers comprises at least one functional hydrophilic chemical group included in the electrode layer stack and arranged to form a covalent bond with a hydroxyl group attached to the electrode layer stack, and the second group of polymers comprises polymers that do not have a functional hydrophilic chemical group.

18. 20. The method of processing an electrode layer stack for manufacturing an electrowetting optical element according to claim 17, wherein the first group of polymers and the second group of polymers are deposited by wet chemical dip coating from corresponding polymer solutions.

19. 19. A method for processing an electrode layer stack for manufacturing an electrowetting optical element as described in claim 17 or 18, wherein, before depositing the second group of polymers, a portion of the deposited first group of polymers is removed by immersing the electrode layer stack in a fluorocarbon solvent arranged to dissolve the first group of polymers, thereby removing any of the first group of polymers that are not covalently bonded to hydroxyl groups contained in and attached to the electrode layer stack.

20. between the step of depositing the first group of polymers and the step of removing a portion of the deposited first group of polymers; 20. A method for processing an electrode layer stack for manufacturing an electrowetting optical element according to any one of claims 17 to 19, further comprising a step of annealing the electrode layer stack comprising the deposited polymers of the first group, the annealing step being carried out at an elevated temperature, preferably above 100°C.

21. before the step of providing the insulating layer, A method for processing an electrode layer stack for the manufacture of electrowetting optical elements according to any one of claims 17 to 20, further comprising the step of chemically activating the first electrode layer to enable covalent bonding with the polymers of the first group.

22. The step of providing the insulating layer is preceded by the following successive steps: providing a support layer on the first electrode layer; chemically activating the surface of the support layer to allow covalent bonding with the first group of polymers in the insulating layer; Further provided with A method for processing an electrode layer stack for the manufacture of an electrowetting optical element according to any one of claims 17 to 21, wherein the support layer comprises one or more materials selected from the group consisting of inorganic non-metallic materials and organic materials having high electrical resistivity, more preferably chemically cross-linked organic materials having high electrical resistivity.

23. A method for treating an electrode layer stack for the manufacture of electrowetting optical elements according to any one of claims 21 to 22, wherein said chemical activation step is carried out by providing hydroxyl groups.

24. 1. A method of processing an electrode layer stack for manufacturing an electrowetting optical element, comprising: providing an electrode layer stack comprising a substrate and an electrode layer; providing cell walls on the electrode layer stack, the cell walls extending from the electrode layer stack and defining a three-dimensional non-planar surface to at least partially define a containment space enclosing a polar liquid and a non-polar liquid; providing an insulating layer on the electrode layer stack over the electrode layers and the cell walls to form an interface with the containment space; Equipped with The insulating layer is formed by the following successive steps: depositing a first group of polymers onto the electrode layer stack; removing a first group of polymers that are not covalently bonded to the electrode layer stack; depositing a second group of polymers onto the electrode layer stack; the first group of polymers and the second group of polymers are formed to be entangled as a polymer network in the insulating layer; A method of processing an electrode layer stack for manufacturing an electrowetting optical element, wherein the first group of polymers comprises at least one functional hydrophilic chemical group included in the electrode layer stack and arranged to form a covalent bond with a hydroxyl group attached to the electrode layer stack, and the second group of polymers comprises polymers that do not have a functional hydrophilic chemical group.

25. Electrowetting optical display comprising one or more electrowetting optical elements according to any one of claims 1 to 16.

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