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    • 专利摘要:
    electric wetting device, method of manufacturing the electric wetting device (200), method of operating the electric wetting device (200) the invention relates to an electric wetting device on dielectric (200). this is an electrical wetting device comprising one or more cells, each cell comprising an electrical wetting composition of the first and second immiscible fluids, the first fluid being an electrolytic solution (240), a first electrode (230), separated from the composition of electrical wetting by a dielectric (231), and a voltage source (260) to apply a difference in operating potential between the first electrode (230) and the electrolytic solution to operate the electrical wetting device. according to the invention, the first electrode (230) of the electric dielectric wetting device (200) comprises a valve metal, and the electrolytic solution (240) is capable of anodizing the valve metal to form a metal oxide in the difference in operating potential. this provides the electrical dielectric wetting device (200) with self-healing properties in this way preventing the collapse of the dielectric. as a result, the electrical damping device can be operated at a low voltage, and has improved reliability.
    公开号:BR112012007656B1
    申请号:R112012007656-6
    申请日:2010-09-29
    公开日:2020-09-24
    发明作者:Stein Kuiper；Johannes Wilhelmus Weekamp
    申请人:Koninklijke Philips N.V.；
    IPC主号:
    专利说明:

    [0001] The invention relates to an electrical wetting device comprising one or more cells, each cell comprising (a) an electrical wetting composition comprising first and second immiscible fluids, the first fluid being an electrolytic solution, (b) a separate, first electrode the composition of electrical wetting by a dielectric, and (c) a voltage source to apply a difference in operating potential between the first electrode and the electrolytic solution to operate the electrical wetting device.
    [0002] The invention also relates to methods of manufacturing and operating the aforementioned electrical wetting device. HISTORY OF THE INVENTION
    [0003] Electrical wetting is an electrostatic control of the contact angle between a liquid and a solid. A potential difference applied between a conductive liquid and a conductive substrate reduces the interfacial energy, which increases the degree of wetting of the substrate by the liquid. Electric wetting can be applied to move and shape volumes of liquids. For example, when a droplet of water is present on a hydrophobic surface, the contact area between the two is minimized. However, when a suitable potential difference is applied between a first electrode that is present below the hydrophobic surface and a second electrode that is placed in the water droplet, the water droplet spreads over the hydrophobic surface (in other words, the hydrophobic properties of the surface appear to decrease). When the potential difference is removed, the water droplet returns to its original state.
    [0004] An electrical wetting device is a device that, in operation, makes use of the electrical wetting effect. Electrical wetting devices are used in a wide range of applications, including variable focus lenses (such as variable focus contact lenses), electronic displays, switches for optical fibers, and micro electromechanical systems (such as micro fluidic devices and devices chip laboratory).
    [0005] Electrical wetting devices typically comprise a cell in which an electrical wetting composition comprising two immiscible fluids, one of which is polar and / or electrically conductive can be manipulated by applying a potential difference between two electrodes.
    [0006] To prevent electrolysis of the electrical wetting composition, one of the electrodes can be separated from the electrical wetting composition by a dielectric means (in the rest of this text simply called a dielectric). Such an electrical wetting device is usually referred to as an electrical over dielectric wetting device (EWOD). The other electrode can be in direct contact with the polar and / or electrically conductive liquid, or it can be capacitively coupled to this liquid.
    [0007] EWOD devices typically have a dielectric that comprises an amorphous fluoro polymer (eg, Teflon® AF), silicon dioxide (SiO2), or parylene polymer (a poly (p-xylylene) that can be deposited through chemical vapor deposition ), or a stack of these layers, having a thickness in the order of micrometers so that a relatively high potential difference (in the order of 100 V) is necessary to operate these devices.
    [0008] To reduce device size and / or power consumption and to be able to use standard electronic components, there is a need for EWOD devices that can be operated at lower voltages.
    [0009] The required operating voltage of an EWOD device can be reduced by increasing the dielectric constant and / or decreasing the thickness of the dielectric, thereby increasing the capacitance of the dielectric.
    [0010] Reducing the thickness of the dielectric leads to a lower operating voltage, but also to a larger electric field within the dielectric, and to a greater probability of micro holes in the dielectric. Below a certain minimum layer thickness, the electrical collapse of the dielectric (also referred to as dielectric collapse) occurs before the desired electrical wetting effect is achieved.
    [0011] EWOD devices that can be operated at a reduced voltage are disclosed in US-2006/0221458 and US-2008/0100905, respectively. These known EWOD devices comprise a container with a polar or conductive liquid material, and a first electrode for applying a voltage to the polar or conductive liquid material through a dielectric. The dielectric is a layer of metal oxide formed by anodizing the first electrode. The thickness of the dielectric can be easily and precisely adjusted by adjusting the voltage that is applied during the anodizing process. In addition, the metal oxides of the comparatively high dielectric constant can be formed by anodizing aluminum and tantalum. In addition, such metal oxides can be made in micro-hole-free layers.
    [0012] A disadvantage of known EWOD devices is that over time the dielectric breakdown can still occur, for example, as a result of mechanical stress, fatigue of the dielectric or ion injection from the fluids during the life of the devices. SUMMARY OF THE INVENTION
    [0013] It is an object of the invention to provide an electrical wetting device that can be operated at a low voltage, and that has improved reliability.
    [0014] It is also an object of the invention to provide a method for making such an electrical wetting device.
    [0015] It is yet another object of the invention to provide a method for operating such an electrical wetting device.
    [0016] According to a first aspect of the invention, the objective is achieved by an electrical wetting device according to the opening paragraph, in which the first electrode comprises a valve metal, and in which the electrolytic solution is capable of anodizing the metal valve to form a metal oxide in the difference of operating potential.
    [0017] Essentially, the electrical wetting device according to the invention comprises an electrolytic capacitor. A capacitor comprises two conductive plates separated by a dielectric medium, and in an electrolytic capacitor one of the "plates" is a metallic anode while the other is an electrolytic solution. An electrolyte solution is a solution of an electrolyte in a solvent, an electrolyte being a chemical compound (such as a salt, acid, or base) that dissociates into electrically charged ions when dissolved in a solvent. An electrolyte solution (also called an electrolyte solution, ionic solution, or simply electrolyte) is an ionic conductor of electricity.
    [0018] In an electrolytic capacitor, the electrolytic solution is able to anodize the metal anode. Usually, the dielectric medium of an electrolytic capacitor is a metal oxide produced from a metal anode in an anodizing process. During this anodizing process, electric current flows from the metal anode through a bath containing an electrolytic anodizing solution to a bath cathode. The flow of electrical current causes an insulating metal oxide to grow outward and onto the surface of the metal anode. The thickness, structure and composition of this insulating metal oxide layer determine its dielectric strength. For this purpose, the anode must comprise a valve metal, being a metal from which an oxide is formed under anodic conditions in an electrolytic cell. Valve metals include magnesium, aluminum, titanium, vanadium, chromium, zinc, zirconium, niobium, antimony, hafnium, tantalum, tungsten and bismuth.
    [0019] In the electrical wetting device according to the invention, the electrolytic capacitor is formed by the first electrode and the electrolytic solution, separated by the dielectric, in which the electrolytic solution (the first fluid in the electrical wetting composition) is an electrolytic anodizing solution.
    [0020] In an electrolytic capacitor, the electrolytic anodizing solution is able to repair and thicken the dielectric medium locally as needed, a process that is driven by the leakage current from the capacitor that is removed when in operation. A similar self-repairing (or curing) mechanism applies to the electrical wetting device according to the invention, resulting in improved device reliability.
    [0021] In the electrical wetting device according to the invention, the dielectric can be a single layer, or a multi-layer structure (a cell). The dielectric can be a metal oxide produced from a metal anode in an anodizing process, although this does not necessarily have to be so. Basically, any dielectric can be used, as long as the combination of the first electrode and the electrical wetting composition provides the electrical wetting device with the self-repair functionality mentioned above. This means that the electrical wetting device according to the invention has an improved reliability even when a dielectric is used that is not obtained by anodizing the first electrode, such as, for example, a dielectric comprising parylene or a polyester such as polyethylene terephthalate (PET). An advantage of using a polyester, such as PET, is that it is an inexpensive material that can be readily structured with a laser excimer. Consequently, it is very well suited for use in low-cost disposable applications, for example, chip lab applications.
    [0022] In the electrical wetting device according to the invention, the first fluid of the electrical wetting composition is an electrolytic anodizing solution capable of anodizing the valve metal of the first electrode to form a metal oxide in the difference in operating potential. In other words, the first fluid is susceptible to an electric field. The second fluid in the electrical wetting device, which is immiscible with the first fluid, is much less susceptible to an electric field than the first fluid. The second fluid can be an oil, for example, silicon oil, or air.
    [0023] The electrolytic anodizing solution can be any solution as used in the electrolytic capacitor, as these solutions provide the self-repair (or cure) mechanism as described above, while maintaining the integrity of the dielectric. In addition, for use in the electrical wetting device according to the invention, the electrolytic anodizing solution does not have to comply with the same requirements as for electrolytic capacitors, therefore a relatively high electrical conductivity is not necessary. Generally, the lower the ion concentration in the electrolytic anodizing solution, the lower the probability of the dielectric collapsing and the higher the reliability of the electrical wetting device.
    [0024] The electrolytic anodizing solution preferably comprises a polar solvent such as water. In addition to water, several other polar solvents can be used, such as polyhydric alcohols, gamma-butyrolactane (GBL), dimethylformamide (DMF), N-methylpyrrolididone (NMP), amides, polypyrrole, molten salts and any combination of these.
    [0025] Particularly preferred electrolytic anodizing solutions are those that result in layers of substantially non-porous anodized metal oxide (or micro-hole free). Examples of such solutions are solutions of citric acid, tartaric acid and boric acid, as well as solutions of ammonium borate, ammonium tartrate and ammonium phosphate.
    [0026] In the electrical wetting device according to the invention, a potential difference is applied between the first electrode and the electrolytic solution (the first fluid in the electrical wetting composition) through a voltage source. Obviously, this can be done by connecting one terminal of the voltage source of the first electrode, and the other terminal to a second electrode that is either directly coupled to the electrolyte solution, or capacitively coupled through an intermediate insulating layer.
    [0027] The second electrode is preferably inert in relation to the electrolytic anodizing solution (the first fluid in the electrical wetting composition). For example, the second electrode can be a stainless steel electrode.
    [0028] In order to achieve an appropriate balance between chemical stability and internal electrical resistance, the first fluid (the electrolytic anodizing solution) can comprise additives such as sugars and / or ethylene glycol.
    [0029] In the electrical wetting device according to the invention, the dielectric can be a stack of layers, wherein the stack comprises a hydrophobic layer that is in contact with the electric wetting composition. Preferably, the hydrophobic layer comprises an amorphous fluoro polymer, such as Teflon®.
    [0030] The dielectric can comprise a layer of metal oxide that has been formed by anodizing the valve metal of the first electrode.
    [0031] The electrolytic anodizing solution can be an acidic solution or an alkaline solution. When the electrical wetting device comprises a Teflon® layer, the use of an acidic solution is preferred, as experiments have shown that alkaline solutions cause negative loading of the surface of the Teflon® layer, due to the preferred adsorption of hydroxyl ions (OH) on hydrogen ions (H3O +). The acidic solutions contain slightly more hydroxyl ions than the alkaline solution, thereby reducing the likelihood of hydroxyl ions adsorption.
    [0032] When the electrolytic anodizing solution is an acidic solution it can comprise an organic acid. Organic acids can either be aliphatic or aromatic organic acids. Aliphatic organic acids either have straight chains, branched chains or non-aromatic rings.
    [0033] Examples of suitable aliphatic organic acids are mono carboxylic organic acids, acetic acid, propionic acid, acrylic acid, and butyric acid. Such organic acids can be used alone, or in combination with salts such as ammonium acid borate, sodium borate, sodium potassium tartrate, ammonium phosphate, sodium acetate or ammonium acetate.
    [0034] Derivatives of mono carboxylic organic acids can also be used, such as lactic acid, hydroxyacrylic acid, crotonic acid, ethylene lactic acid, dehydroxy propionic acid, isobutyric acid, diethyl acetic acid, isoamyl acetic acid and isobutyl acetic acid.
    [0035] After monocarboxylic organic acids, multi carboxylic acids can also be used, such as organic dicarboxylic acid, tartaric acid and tricarboxylic citric acid.
    [0036] Examples of suitable aromatic organic acids are creyulic acid (cresol) and carbolic acid (phenol).
    [0037] After organic acids, inorganic acids can also be used, either alone or in combination with an organic acid. An example of a suitable inorganic acid is boric acid.
    [0038] A preferred acid is an acid chosen from the group consisting of citric acid, tartaric acid and boric acid, as an electrolytic anodizing solution comprising such an acid results in non-porous (or micro-hole free) anodized metal oxide layers.
    [0039] In the electric wetting device according to the invention, the first fluid of the electric wetting composition can comprise a salt, preferably a salt chosen from the group consisting of borates, tartrates, citrates and phosphates, since they result in layers of oxide of anodized metal substantially non-porous (or free of micro holes).
    [0040] In the electrical wetting device according to the invention, the valve metal of the first electrode can be chosen from the group consisting of magnesium, aluminum, titanium, vanadium, chromium, zinc, zirconium, niobium, antimony, hafnium, tantalum, tungsten and bismuth.
    [0041] In the case of a micro hole in the dielectric, the self-repair mechanism will start. During this process, hydrogen gas is created at the anode (the first electrode). Small amounts of this gas can dissolve, but larger amounts will cause pressure, and can disrupt the functioning of the electrical wetting device, particularly when the device has a lens function. This problem can be solved by making a pressure relief valve, or by adding a hydrogen trap in the electrolyte solution. Examples of suitable hydrogen scavengers are aromatic amino and nitro salts, typically in concentrations of 1%.
    [0042] According to a second aspect of the invention, the objective is achieved through a method of fabricating the above electrical wetting device, comprising the step of forming the dielectric by anodizing the valve metal of the first electrode.
    [0043] According to a third aspect of the invention, the objective is achieved through a method of operating the above electrical wetting device, comprising the step of applying a potential difference between the first electrode and a second electrode, so that a positive voltage medium time liquid is applied to the first electrode. The method of operation preferably uses DC voltages with the first electrode having a positive polarity to allow anodization. In addition, if the dielectric comprises a metal oxide, the use of DC voltages prevents the dissolution of the metal oxide. However, AC voltages can also be used to prevent the dielectric from charging. If the AC conduction is performed in such a way that, on average, a positive net voltage is applied to the first electrode, the metal oxide included in the dielectric must not dissolve.
    [0044] An alternative method for applying AC voltages to the electrical wetting device according to the invention is to use a capacitor in series with the device, so that the so-called back-to-back configuration is created. In other words, in addition to a voltage source, a capacitor is inserted between an electrode and the electrical wetting composition. This method is known to conduct electrolytic capacitors with an AC voltage. BRIEF DESCRIPTION OF THE DRAWINGS
    [0045] Figs. 1a and 1b show a cross section of a cell that can be comprised in an electrical wetting device according to the present invention. Figs. 2a and 2b show cross sections of an example of an electrical wetting device according to the invention in the form of a variable focus lens. DETAILED DESCRIPTION OF ACHIEVEMENTS
    [0046] Figs. 1 and 2 show cross sections of several cells that can be comprised in an electrical wetting device according to the present invention. In Fig. 1, cell 100 comprises an electrical wetting composition of a first fluid 110 and a second fluid 120. The first fluid 110 is immiscible with the second fluid 120. In addition, the first fluid 110 is an electrolyte solution. Cell 100 further comprises a first electrode in the form of an aluminum layer 130, aluminum being a valve metal, and is separated from the electrical wetting composition by the dielectric in the form of a cell comprising a layer of parylene 140, and a hydrophobic coating. 150, where the latter is in contact with the electrical wetting composition.
    [0047] Cell 100 also comprises a DC voltage source in the form of a battery 160, from which the positive terminal is connected with the aluminum layer 130, and the negative terminal to the first fluid 110. In Fig. 1a no voltage is applied, while in Fig. 1b a difference in operating potential is applied between the aluminum layer 130 and the first fluid 110. Consequently, the electrical wetting effect is obtained as illustrated by the change in the interface between the first fluid 110 and the second fluid 120, caused by electromechanical forces, leading to an apparent change in the hydrophobic properties of the hydrophobic coating 150. In this difference in operating potential, the first fluid 110, being an electrolytic solution, is capable of anodizing the aluminum of the aluminum layer 130 to form oxide aluminum.
    [0048] Alternatively, a cell such as that shown in Fig. 1 may have a dielectric which, instead of the parylene layer 140, comprises a metal oxide layer, preferably an aluminum oxide layer which is obtained by anodizing the aluminum 130, or a layer of polyethylene terephthalate (PET). In addition, the aluminum layer 130 can be provided on a conveyor, such as a glass conveyor or a silicon conveyor.
    [0049] Fig. 2 shows cross sections of a variable focus lens 200, an example of an electrical wetting device according to the invention.
    [0050] The variable focus lens 200 comprises a first transparent substrate 210, a second transparent substrate 220, and a metallic spacer 230 moving away from the first transparent substrate 210 and the second transparent substrate 220. The first transparent substrate 210, the second transparent substrate 220, and the metal spacer 230 constitutes a cell containing an electrical wetting composition, comprising an aqueous electrolytic solution 240 and an oil 250, both with different optical properties.
    [0051] The metal spacer 230 is the first variable-focus lens electrode 200, comprises a valve metal, and is coated with a dielectric in the form of a metal oxide layer 231, separating the metal spacer 230 from the electrical wetting composition. The first transparent substrate 210 is coated with another electrode in the form of a hydrophilic conductive transparent coating 211.
    [0052] The areas of the second transparent substrate 220 and the metal oxide layer 231 that are exposed to the electrical wetting composition are coated with a transparent hydrophobic coating 221. The transparent hydrophobic coating 221 is also applied to the second substrate 220 in order to prevent any conductive liquid to condense on the second substrate 220.
    [0053] The variable focus lens 200 also comprises a DC voltage source in the form of a battery 260, of which the positive terminal is connected to the metal spacer 230, and the negative terminal to the hydrophilic conductive coating 211. The negative terminal is preferably buried, the in order to keep the electrolytic solution 240 at the same potential as the surrounding ones, thereby preventing potential differences between the electrolytic solution 240 and the surrounding ones from distorting the fluid-fluid interface. In Fig. 2a no voltage is applied, while in Fig. 2b a difference in operating potential is applied between the metallic spacer 230 and the hydrophilic conductive coating 211. Consequently, the electrical wetting effect is obtained as illustrated by the change in the interface between the aqueous electrolytic solution 240 and the oil 250, caused by a change in the hydrophobic properties of the hydrophobic coating 221. In this difference in operating potential, the aqueous electrolytic solution 240 of the electrical wetting composition is capable of anodizing the valve metal of the metallic spacer 230 to form a metal oxide.
    [0054] An electrical wetting device according to the invention can be manufactured as follows.
    [0055] An aluminum substrate is placed in an aqueous solution of 8% citric acid and 0.5% phosphoric acid. The anodizing of the aluminum substrate is performed by applying a potential difference between the aqueous solution and the aluminum substrate, with the aluminum substrate forming the anode, while the cathode consists of a stainless steel plate. The density of the electric current is about 10 mA / cm2, the initial anodizing voltage is lower than 150 V, and the final anodizing voltage is 150 V. After several hours, a layer of aluminum oxide with a thickness of 210 nm grows on the aluminum substrate.
    [0056] Preferably, the pH of the aqueous citric acid solution is increased to prevent the cauterization of aluminum and aluminum oxide when no tension is applied to the device, while maintaining the anodizing capacity and good performance of electrical wetting. The pH of the aqueous citric acid solution can be increased by adding an ammonium hydroxide solution. For example, the pH of one liter of 8% aqueous citric acid solution can be increased by adding 0.18 liters of a 5 M ammonium hydroxide solution to obtain a pH of 6.68.
    [0057] As a dielectric layer obtained through anodizing can be porous, after anodizing a sealing process can be performed to make the dielectric layer free from micro holes.
    [0058] The aluminum oxide layer is then coated with a 10 nm layer of Teflon® AF-1600 amorphous fluoro polymer by immersing the coating in a 1% solution of Teflon® AF-1600 in FC-75 (a derivative of fluoro carbon of tetrahydrofuran, with chemical formula C8F16O). The amorphous fluoro polymer coating is annealed at 200 ° C for 10 minutes to evaporate any remaining solvent. The deposition of the coating can also be done with gas anodization, using an oxygen plasma, or with deposition of the atomic layer.
    [0059] Next, a drop of an 8% aqueous solution of citric acid, surrounded by silicon oil, is provided in the amorphous fluoro polymer coating.
    [0060] The above has resulted in an electric wetting device according to the invention, in which the first fluid of the electric wetting composition is an electrolytic solution in the form of an 8% aqueous solution of citric acid, and the second fluid of the composition of Electric wetting is silicon oil, both fluids being immiscible. The first electrode is the aluminum substrate, which is separated from the electrical wetting composition by a dielectric in the form of a stack of 210 nm thick aluminum oxide layer and the 10 nm thick Teflon® AF-1600 layer .
    [0061] When the aluminum substrate is connected to the positive terminal of a voltage source, and the drop of an 8% aqueous solution of citric acid, surrounded by silicon oil, is connected to the negative terminal of the voltage source, operating voltages between 0 V and 2 0 V are obtained, since these potential differences clearly show the effect of electrical wetting on this the drop spreads after the increase in the potential difference. Even after deliberately scratching the stack of layers, penetrating through the entire stack, the electrical wetting effect continues without the dielectric collapse.
    [0062] Similar devices can also be made from substrate comprising magnesium, aluminum, titanium, vanadium, chromium, zinc, zirconium, niobium, antimony, hafnium, tantalum, tungsten, and bismuth, in which a corresponding metal oxide layer may be growing through anodizing.
    [0063] The dielectric can be supplied by spraying, evaporating, annealing a paste, depositing the atomic layer from a gaseous precursor, depositing the chemical vapor, thermal oxidation, eloxation, or anodizing.
    [0064] In an anodizing process, the applied potential difference determines the thickness of the dielectric. For example, for an aluminum oxide layer the possible thickness is 1.4 nm / V, and for the tantalum oxide layer 2 nm / V.
    [0065] The inventors have realized that, for a certain thickness of the dielectric, the voltage used to operate the electrical wetting device is much lower than the voltage required to grow the dielectric through anodizing the first electrode. This implies that the dielectric does not grow during the operation of the electrical wetting device. Only in the event of a failure in the dielectric will the growth process begin, but the dielectric will not become thicker than it was originally designed. For example, an electrical wetting device comprising dielectric in the form of a 100 nm tantalum oxide layer is typically operated at a 10 V operating voltage, while the tantalum oxide layer has grown by 50 V. For thicker dielectrics , the difference becomes even greater due to the dependence of the square root on the conduction voltage of the electrical wetting in the thickness of the dielectric, as compared to the linear dependence of the dielectric thickness on the anodizing voltage.
    [0066] Particularly when the dielectric comprises a metal oxide layer, the electrical wetting device according to the invention is preferably operated with DC voltages with the first electrode having a positive polarity to allow anodizing, to prevent the dissolution of the oxide layer. metal.
    [0067] However, to prevent the dielectric from charging, it is advantageous to use AC voltages. The AC conduction is preferably performed in such a way that, on average, the positive net voltage is applied to the first electrode, to prevent the dielectric from dissolving. Load formation can now be prevented by scanning the voltage between a high positive value (working point) and a low value (discharge point), for example, 0 V.
    [0068] A first way of using AC conduction so that on average a net positive voltage is applied to the first electrode, is by adding positive voltage compensation to the AC conduction voltage.
    [0069] By adding positive compensation to the AC voltage, the average voltage can be positive while the constructed load can be removed with a negative voltage. There may be competition between an anodizing process during the application of a positive voltage and a dissolution process during the application of a negative voltage. These processes are dependent on the duration and magnitude of the applied voltages. When the positive compensation is very low, the dissolution process can win and the anodized layer could be destroyed. Or, if there is still no anodized layer (for example, in the case of perforated parylene deposited on aluminum), no anodized layer will be formed. When the positive compensation is very high, the anodizing process can win, but the removal of charge by applying a negative voltage could be less effective.
    [0070] Experiments have shown that the compensation in which the anodizing process only beats the dissolution process is frequency dependent, with a lower frequency requiring a higher DC compensation to reach the point where the dissolution and anodizing process are equally strong.
    [0071] For example, an experiment was performed using an 8% solution of aqueous citric acid, surrounded by silicon oil, in a perforated parylene coating C having a thickness of 300 nm deposited on aluminum. Table 1 gives the DC compensation in which the anodizing and dissolving processes are equally strong (DC compensation limit), as a function of the AC conduction frequency. In Table 1, the DC compensation is also given as a percentage of the maximum voltage amplitude, which is 7 V in this experiment.
    [0072] Table 1: The DC compensation limit has an AC conduction frequency function, for a device using an 8% aqueous citric acid solution, surrounded by silicon oil, in a perforated parylene coating C having a thickness of 300 nm deposited in aluminum.
    [0073] Higher frequencies may require only relatively small compensation, or even no compensation at all. For example, when the aforementioned device is conducted with an AC frequency of around 1000 Hz, no compensation is necessary. Theoretically, it could be possible that even the AC conduction with a relatively small negative compensation would still allow anodizing, in the case of the anodizing process it is more effective than the dissolution process.
    [0074] A second way to use the AC conduction so that on average a positive net voltage is applied to the first electrode, is to perform the AC conduction using a modified duty cycle. As already mentioned above, the competition of the anodizing and solution processes are dependent on the duration and magnitude of the applied voltages. When the length of the period in which a positive voltage is applied is relatively short compared to the length of the period in which a negative voltage is applied, the dissolution process can gain and the anodized layer could be destroyed. Or, if there is still no anodized layer (for example, in the case of perforated parylene deposited on aluminum), no anodized layer will be formed. If the length of the period in which a positive voltage is applied is relatively long, the anodizing process may win, but the removal of charge during the (relatively short) period in which a negative voltage is applied could be less effective.
    [0075] For example, an experiment was performed using an 8% solution of aqueous citric acid, surrounded by silicon oil, in a perforated parylene coating C having a thickness of 300 nm deposited on aluminum. Table 2 gives the cycle (fraction of time when a positive voltage is applied) in which the dissolution and anodizing processes are equally strong (duty cycle limit), as a function of the AC conduction frequency.
    [0076] Table 2: Duty cycle limit as a function of the AC conduction frequency, for a device using an 8% solution of aqueous citric acid, surrounded by silicon oil, in a perforated parylene coating C having a thickness of 300 nm deposited on aluminum.
    [0077] Depending on the choice of materials and conditions, AC conduction can effectively be used to prevent charging. For the aforementioned device, the fraction of time that a positive voltage is applied is preferably 50% or more when AC conduction frequencies of about 250 Hz or less are used. For higher AC conduction frequencies, the fraction of time that a positive voltage is applied can be lower than 50%.
    [0078] Theoretically, a duty cycle in which the length of the period in which a positive voltage is applied is shorter than the length of the period in which a negative voltage is applied can still allow anodizing when the anodizing process is more effective than the process dissolution.
    [0079] The terms "first", "second", and similar in the description and in the claims, are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order. It is to be understood that the terms then used are interchangeable in appropriate circumstances and that the embodiments of the invention described here are capable of operating in sequences other than those described or illustrated here.
    [0080] It should be realized that the above-mentioned achievements illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative achievements without departing from the scope of the pending claims. In claims, any reference signs placed in parentheses should not be construed as limiting the claim. The use of the verb "to understand" and its conjugations does not exclude the presence of elements or steps beyond those established in a claim, nor does it exclude the realizations in which the verb means "to consist of". The article "one" or "one" preceding an element does not exclude the presence of the plurality of such elements. The mere fact that certain measures are cited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.
    权利要求:
    Claims (14)
    [0001]
    ELECTRIC WETTING DEVICE (200) comprising one or more cells, each cell comprising: - an electrical wetting composition, comprising first (240) and second (250) immiscible fluids, the first fluid (240) being an electrolytic solution, - a first electrode (230), separated from the electrical wetting composition by a dielectric (231), and - a voltage source (260) to apply a difference in operating potential between the first electrode (230) and the electrolytic solution (240) to operate the electrical wetting device (200), characterized by: - the first electrode (230) comprises a valve metal, and - the electrolytic solution (240) is capable of anodizing the valve metal to form a metal oxide with no difference in operating potential.
    [0002]
    ELECTRIC WETTING DEVICE (200), according to claim 1, characterized in that the dielectric (231) is a cell, the cell comprising a hydrophobic layer (221) which is in contact with the electric wetting composition.
    [0003]
    ELECTRIC WETTING DEVICE (200), according to claim 2, characterized in that the hydrophobic layer (221) comprises an amorphous fluoro polymer.
    [0004]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 3, characterized in that the dielectric (231) comprises a metal oxide layer formed by anodizing the valve metal of the first electrode (230).
    [0005]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 3, characterized in that the dielectric (231) comprises parylene.
    [0006]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 5, characterized in that the electrolytic solution (240) comprises an acid.
    [0007]
    ELECTRIC WETTING DEVICE (200) according to claim 6, characterized in that the acid is an organic acid.
    [0008]
    ELECTRIC WETTING DEVICE (200), according to claim 6, characterized in that the acid is chosen from the group consisting of citric acid, tartaric acid and boric acid.
    [0009]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 5, characterized in that the electrolytic solution (240) comprises a salt.
    [0010]
    ELECTRIC WETTING DEVICE (200), according to claim 9, characterized in that the salt is chosen from the group consisting of borates, tartrates, citrates and phosphates.
    [0011]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 10, characterized in that the valve metal is chosen from the group consisting of magnesium, aluminum, titanium, vanadium, chromium, zinc, zirconium, niobium, antimony, hafnium , tantalum, tungsten and bismuth.
    [0012]
    ELECTRIC WETTING DEVICE (200) according to any one of claims 1 to 11, characterized in that the electrolytic solution (240) comprises a hydrogen trap.
    [0013]
    METHOD OF MANUFACTURING THE ELECTRIC WETTING DEVICE (200), as defined in any of claims 1 to 12, characterized by comprising the step of forming the dielectric (231) by anodizing the valve metal of the first electrode (230).
    [0014]
    METHOD OF OPERATING THE ELECTRIC WETTING DEVICE (200), as defined in any of claims 1 to 12, characterized by comprising the step of applying a potential difference between the first electrode (230) and the electrolytic solution (240), of so that a positive net voltage mediated by time is applied to the first electrode (230).
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    法律状态:
    2017-10-10| B25D| Requested change of name of applicant approved|Owner name: KONINKLIJKE PHILIPS N.V. (NL) |
    2017-10-24| B25G| Requested change of headquarter approved|Owner name: KONINKLIJKE PHILIPS N.V. (NL) |
    2019-01-08| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2019-07-16| B06T| Formal requirements before examination|
    2019-10-08| B07A| Technical examination (opinion): publication of technical examination (opinion)|
    2020-04-22| B09A| Decision: intention to grant|
    2020-09-24| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 29/09/2010, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    EP09172296.7|2009-10-06|
    EP09172296|2009-10-06|
    PCT/IB2010/054378|WO2011042835A1|2009-10-06|2010-09-29|Electrowetting device|
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