Patent Application
20230324799
Devices such as batteries, sensors, photovoltaics, and others rely on the flow of ions during their operation. This may be achieved by using a liquid electrolyte, e.g. a liquid comprising dissolved ions that allows the flow of ions. However, such electrolytes can suffer leakage and/or evaporation, which in turn affects the conductivity required for a given purpose. It is desirable to mitigate such problems.
Examples described herein relate to a resist mixture which can be used to form a material through which ions can flow for conducting electricity.
In some examples a resist mixture comprises a crosslinker for reducing mobility of a polymer to which at least one of a cationic component or an anionic component is bonded; such examples are referred to below as a first class of examples.
In examples of the first class, the resist mixture is crosslinkable and comprises: a polymer comprising siloxane; a crosslinker; and a salt comprising a cationic component, and an anionic component. At least one of the cationic component or the anionic component of the salt is bonded to the polymer, for example, directly by a covalent bond or by a linker which is covalently bonded to at least one of the cationic component or the anionic component of the salt and to the polymer. The bond between the polymer and the component of the salt e.g. reduces leakage or leaching of the salt and/or the potential washing away of the salt during any development or solvent washing step after cross linking. Further, by maintaining ionic sites within the crosslinked material to which ions (the other of the cationic or anionic component not bonded to the polymer, and which component flows to provide an electrical/ionic current) can be attracted, the crosslinked material can maintain its ion-conductive properties for a longer period of time compared with a leachable electrolyte, which can increase the usable lifetime of a device (e.g. an electromechanical device incorporating the crosslinked and/or immobilised material). Further, it has been realised that in examples, the glass transition temperature of the polymer is 260 Kelvin or less, which at room temperature (298 K), gives freely mobile ions within the substance. In some examples, such as at a glass transition temperature of 230 Kelvin or less, or 200 Kelvin or less, there is improved free ion mobility compared with higher glass transition temperatures. In examples, the amphiphilic nature of the polymer results in the formation of phase-separated domains in which the ions can flow. In some examples, crosslinking the resist mixture reduces mobility of the polymer chains, e.g. substantially immobilises the polymer chains such that the material can be considered quasi- or solid-state. Such properties give useful ion-conductivity and physical properties for various purposes.
In examples of the first class, the resist mixture is patternable by, for example, crosslinking one or more regions of the resist mixture after the mixture is deposited on a substrate. Then, other regions of the mixture which were not crosslinked can be removed to leave behind the crosslinked regions patterned as desired for a given purpose, e.g. for a given electromechanical device requiring a patterned structure with electrical conductivity. Hence the resist mixture can be considered to be a mixture which functions as a resist, in that the resist mixture can be treated under certain chemical and/or physical conditions to harden, solidify or otherwise change chemical and/or physical properties so as to be useful for patterning when deposited on a substrate. Where for example the treated resist remains on the substrate while removing untreated regions of the resist, the resist can be referred to as a negative resist.
Such chemical and/or physical treatment of the resist mixture is e.g. exposing the resist mixture to electromagnetic radiation such as light (e.g. ultraviolet light) in the case of a photoresist, or to radiation such as an electron beam, or to heat. Such exposure causes crosslinking of the mixture such that the crosslinked material is sufficiently insoluble to a solvent or other developer material used to remove regions of the deposited mixture which were not selected to be crosslinked.
A second class of examples is also referred to herein, which are similar in functionality to examples of the first class in respect of reducing mobility of the polymer to which at least one of the cationic component or the anionic component is bonded, except that instead of, or in addition to, a crosslinker in the resist mixture being used to reduce mobility of the polymer to which at least one of the cationic component or the anionic component is bonded, a monomer in the resist mixture is polymerised in order to reduce mobility or immobilise the polymer to which at least one of the cationic component or the anionic component is bonded. The polymerised monomer is a polymer different from the first polymer and comprises a siloxane or a non-siloxane and may also comprise a cationic or anionic component bonded to it. In some examples, the polymerisable monomer in the second class of examples can also itself, additionally be crosslinkable to further reduce the mobility of the polymer to which at least one of the cationic component or the anionic component is bonded. Further details of examples particular to the first class, and separately to the second class are described below. But it is to be appreciated that certain functionalities apply both to the first and second classes of examples.
In examples of the second class, the resist mixture is polymerisable and comprises at least: a polymer comprising siloxane; a monomer; and a salt comprising a cationic component, and an anionic component. Similar as for examples of the first class, at least one of the cationic component or the anionic component of the salt is bonded to the polymer. The polymerisable resist mixture is patternable similarly as described for the examples of the first class, except that instead of, or in addition to, crosslinking, the resist mixture polymerises by polymerising the monomer, e.g. by chemical and/or physical treatment such as exposing the resist mixture to electromagnetic radiation such as light. In some examples, the polymerisable resist mixture comprises a crosslinker, which in some examples is separate from the monomer in the mixture, and in other examples is part of the monomer (e.g. a crosslinker is covalently bonded to the monomer and/or the monomer comprises the crosslinker). The polymerisation of the monomer and the crosslinking of the crosslinker (e.g. between chains of the polymerised monomer, or between chains of the polymer with at least one of the cationic component or the anionic component bonded to the polymer, or between chains of each of the polymerised monomer and chains of the polymer with at least one of the cationic component or the anionic component bonded to the polymer) can be considered to form a molecular network which reduces mobility, e.g. by entanglement, of the polymer which has the at least one of the cationic component or the anionic component bonded thereto. Crosslinking can occur either during the polymerisation reaction of the monomer, or instead after the polymerisation of the monomer has occurred. In other examples without a crosslinker (either separate from the monomer in the mixture or part of the monomer), the polymerised monomer itself can reduce mobility of the polymer with the at least one of the cationic component or the anionic component bonded thereto.
In some examples of the first and second classes, the polymer comprising siloxane is referred to as a first polymer, and the mixture further comprises a second polymer different from the first polymer. Note that the term second polymer is used to refer to a different polymer than the polymerised monomer described herein for the second class examples. The second polymer is a non-siloxane polymer or a siloxane polymer different from the first polymer. This second polymer in some examples has a crosslinker (e.g. similar to those described in other examples) covalently bonded to it, which can be used to crosslink second polymer chains together in the mixture.
As will be appreciated, a crosslinker can be considered a molecule or chemical group which is reactive (e.g. by appropriate initiation) to bond two or more polymer chains together, to form a crosslinked material from the resist mixture, and thus can be distinguished from a monomer which undergoes a polymerisation reaction to form a polymer chain. By use of a crosslinker, in some examples a chain of the first polymer is bonded to another chain of the first polymer, in other examples a chain of the second polymer is bonded to another chain of the second polymer, in further examples a chain of the first polymer is bonded to a chain of the second polymer, and in yet further examples a chain of the first polymer or the second polymer is bonded to a chain of the polymerised monomer. The method of crosslinking is usually determined by the crosslinking chemistry chosen. The density and resulting physical properties (e.g. glass transition, solvent resistance and/or hardness) of the material depends for example on the molecular nature of the crosslinker and how many reactive sites are available for bonding. The extent of crosslinking depends not just on the particular molecular structure of the crosslinker, but in some examples also on the extent of initiation (e.g. the duration or intensity of exposure of the mixture to light or heat).
The crosslinked and/or polymerised material of examples can be considered an ion-conductive material, in that the anionic or cationic component of the salt, which respectively can be considered anions or cations, not bonded to the polymer can flow. This can be considered an ionic conductivity, in that ions are conductible through the material, e.g. to provide an electrical and/or ionic current. In examples the crosslinked or polymerised material has sufficient ion-conductivity without also needing a solvent, plasticiser or any electrolyte unbonded to the polymer.
In some examples, the salt comprises at least one of a carbon-carbon bond or a carbon-hydrogen bond, and so in examples may be considered an organic salt. The salt is, in some examples, an ionic liquid. An ionic liquid referred to herein is for example, when isolated, a liquid or glass at 373 Kelvin. In some examples the salt comprises at least one of a zwitterion, a multi-cation or a multi-anion.
The crosslinked or polymerised material can in some examples be considered a solid-state ion-conductor, in that the material is substantially solid yet still ion-conductive. Substantially solid-state includes examples not just of fully solid-state crosslinked or polymerised material but also material which is not entirely solid, but which is predominantly solid or more solid than liquid (homogeneously throughout the material) as well as materials which are a so-called quasi-solid-state ion-conductor, for example a gel, a semi-solid or a glass. In some examples such materials contain no or substantially no (within functional tolerances) leachable free liquid or solvent which contribute to ion and/or electrical conductive properties of the material. This is desirable as it allows the ion-conductor to be more resistant to degradation and reduces the leaching of substances from the ion-conductor.
More detailed examples will now be described with appropriate reference to the Figures.
though different linkers are envisaged in further examples. The choice of the properties of the linker, such as length, allow the tuning of the conductivity and morphology of any ion channels when the mixture is crosslinked. The polymer 100 when combined with a crosslinker gives a crosslinkable resist mixture of examples described herein, e.g. for manufacturing anion-conductor. In some examples the salt comprises a zwitterion, a multi-cation, or multi-anion (eg. cationic functionalised imidazolium such as butyl-methyl-imidazol-2-ylidene borane, others are envisaged) which allow different ion channel structures and allow modification of the ionic conductivity. A person skilled in the art will appreciate that the terms n, m, and o in
An example polymer 200 of a crosslinkable resist mixture e.g. for manufacturing an ion-conductor is schematically illustrated by
different linkers are envisaged. In some examples the crosslinker is crosslinkable by a catalytic reaction, for example, crosslinkers which are crosslinkable by a photoinitiated alkyne-azide click reaction.
A slash symbol “/” through a bond is used in
An example polymer 400 for a crosslinkable resist mixture e.g. for manufacturing an ion-conductor when mixed with a crosslinker is schematically illustrated in
In some examples the mixture comprises a monomer, for example, 1,6-hexanedioldiacrylate, though different monomers are envisaged in further examples. As will be appreciated, a monomer can be considered a molecule which undergoes a polymerisation reaction to form a polymer chain. In examples the monomer is polymerised to form a polymer, for example poly(1,6-hexanedioldiacrylate), though other polymers are envisaged in other examples. In some examples the polymer bonded to at least one of the cationic component or the anionic component has reduced mobility (e.g. is immobilised and/or cannot be removed from the mixture by being dissolved in a solvent), because it is entangled or otherwise immobilised with the polymerised monomer.
In some examples, the mixture comprises a second polymer, for example a polystyrene, a polyacrylate or a polysiloxane. In some examples the second polymer comprises a crosslinker, for example: a polyester functionalised with an acrylate, a urethane functionalised with an acrylate, or an olefin; other polymers comprising a crosslinker envisaged. A person skilled in the art will appreciate that in some examples the crosslinker requires a catalyst, a photoinitiator and/or sensitizer to be crosslinked. In some examples the mass ratio of the first polymer to the second polymer is between 1:100 and 100:1, in further examples the mass ratio of the first polymer to the second polymer is between 1:5 and 5:1. The second polymer in some examples comprises siloxane, and in other examples the second polymer is a non-siloxane polymer (in other words a polymer without siloxane). In some examples, when the second polymer is crosslinked, the first polymer is reduced in mobility, e.g. immobilised and/or the first polymer cannot be removed from the crosslinked second polymer by being dissolved in a solvent. In other examples, when the second polymer is crosslinked, the first polymer is not immobilised and/or the first polymer can be removed from the crosslinked second polymer by being dissolved in a solvent.
In some examples the mixture comprises a polymerisable and crosslinkable monomer, for example, SU-8, illustrated below:
different monomers are envisaged in further examples.
In some examples, the mixture comprises several different monomers which are polymerisable and crosslinkable. For example, the mixture comprises a first formulation comprising 50 wt% (a person skilled in the art will appreciate the use of weight percent) trimethyloylpropane triacrylate, 20 wt% 1,6-hexanediol diacrylate, 25 wt% acrylic acid, and a 5 wt% photoinitiator; trimethyloylpropane triacrylate 1,6-hexanediol diacrylate and acrylic acid are illustrated below.
The first formulation is mixed with a second formulation comprising the first polymer and the salt to form the mixture. A further example of a first formulation is a 50 wt% polyurethane acrylate and 45 wt% trimethylolpropane triacrylate and 5 wt% photoinitiator. In some examples the mass ratio of the first formulation to the second formulation is between 1:100 and 100:1, in further examples the mass ratio of the first formulation to the second formulation is between 1:5 and 5:1.
Some examples of a mixture of the present disclosure contain a plurality of different polymers, for example, each having the general formula of one of
In examples, such as those of
A crosslinked material, e.g. an ion-conductor is produced by depositing and crosslinking a mixture produced by mixing polymer 740 with 10 wt% pentaerythritol tetraacrylate and 5 wt% 2,2-dimethoxy-1,2-diphenylethanone. The mixture is e.g. deposited on the substrate by spin coating the mixture on to a substrate at 3000 RPM for one minute. A region of the mixture on the substrate is crosslinked by exposing the region to UV light through a photomask for 30 seconds. The region of the mixture that has not been crosslinked by the UV radiation is dissolved and removed using isopropanol.
In examples, such as those of
A crosslinked material such as a solid-state ion-conductor is produced by depositing and crosslinking a mixture of polymer 860 and 1,2-bis(2-mercaptoethoxy)ethane at a 1:1 ratio of thiol to -ene and 2 wt% 2,2-dimethoxy-1,2-diphenylethanone. The mixture is deposited on a substrate by spin-coating the mixture on to the substrate at 3000 RPM for one minute. A region of the mixture on the substrate is crosslinked by is exposing the region to UV radiation through a photomask for 30 seconds. The region of the mixture that has not been crosslinked by the UV radiation is dissolved and removed using acetone. In other examples, the addition of 1,2-bis(2-mercaptoethoxy)ethane is forgone as polymer 860 already comprises a crosslinker.
In examples, the crosslinkable or polymerisable mixture is e.g. for manufacturing an ion-conductor and comprises an additive or additives to modify the properties of the mixture or the mixtures when it has been crosslinked. In some examples additives such as butyl acrylate are added to the mixture to modulate the density of crosslinks when the mixture is crosslinked and/or plasticisers such as triethyleneglycol methylether methacrylate are added to plasticise the mixture and/or the mixture when it is crosslinked. In some examples the plasticiser is a reactive plasticiser, for example butyl acrylate, triethyleneglycol acrylate or siloxane acrylate. In other examples the plasticiser is a nonreactive plasticiser, for example propylene glycol or 1-ethyl-3-butyl-imidazolium tetrafluoroborate. Other plasticisers are envisaged. Changing the density of crosslinks or plasticising the mixture allows modification of the physical properties of the crosslinked mixture. Some examples of the mixture comprise a catalyst, a photoinitiator and/or sensitiser to allow and/or assist the crosslinking and/or polymerisation of the mixture.
Some examples allow the modification of the electronic and/or ionic properties of the mixture or of the crosslinked mixture by the addition of a redox active additive, e.g. vinyl ferrocene. This allows the tuning of the electronic and/or ionic properties, for example for applications as an electrolyte.
In examples, the resist mixture comprising one or more additive to modify one or more properties of the mixture or resulting crosslinked / polymerised mixture. Such properties include for example electronic, catalytic, mechanical, optical, mass transport or processing properties. Such an additive is for example metallic, semiconducting, insulating, or non-metallic, and/or comprises nanoparticles, microparticles, clusters, fillers, nanotubes, a clay, graphene, quantum dots, and/or carbon such as carbon black or graphite. Such an additive, e.g. fillers, is present in the range of for example 0.0001 wt% to 98 wt%, such as 0.01 wt% to 30 wt%.
In some examples the crosslinkable resist mixture for manufacturing an ion-conductor comprises a chromophore. For some examples a chromophore will modulate electromagnetic radiation applied to the mixture, which in some examples allows more efficient crosslinking. In examples, a chromophore is used to provide fluorescent properties to the at least partially crosslinked ion-conductor. The chromophore is, for example, a rhodamine or a rhodamine derivative; however other chromophores are envisaged depending on the desired electromagnetic properties.
Many different examples of polymer mixtures are envisaged that possess ionic functionality and/or crosslinking functionality, as siloxane polymers with a variety of functional groups for crosslinking or suitable for attachment of a component of a salt are commercially available. Many different examples of salts and crosslinkers are envisaged as many suitable salts and crosslinkers are commercially available. In some examples, the crosslinker in the mixture is not bonded to the polymer. In some examples, the crosslinker in the mixture is bonded to the polymer, allowing the polymer to crosslink with itself. A person skilled in the art will also appreciate that any of the polymers referred to herein can be, for example, a simple polymer, a dendrimer, and/or a copolymer of various configurations such as block, diblock, triblock, random, alternate, and/or graft copolymers.
In some examples the mixture comprises a plurality of different crosslinkers, in some examples the different crosslinkers are crosslinkable by different reaction pathways. In some examples both the first polymer and the second polymer are crosslinkable. For example, the mixture comprises polymer 640, a polyurethane acrylate and a combination of photoinitiator, other such mixtures are envisaged. In some examples of such mixtures a plurality of crosslinking mechanisms occur.
In some examples the mixture comprises a polymer wherein a first crosslinker is covalently bonded to the polymer; and a second crosslinker. For example, the mixture comprises polymer 860 and SU-8, other examples are envisaged. In such examples, upon irradiation of this mixture a plurality of crosslinking mechanisms are envisaged. In some examples the mass ratio of the polymer to the monomer is between 1:100 and 100:1, in further examples the mass ratio of the polymer to the monomer is between 1:5 and 5:1.
In some examples, the crosslinkable resist mixture is e.g. for manufacturing an ion-conductor and comprises a surfactant. The surfactant is, for example, non-ionic (e.g. polysorbate), anionic (e.g. sodium lauryl sulfate), cationic (e.g. benzalkonium chloride), or amphoteric (e.g. cocoamidpropl betaine). The surfactant allows the modification of structure of ion channels that are produced within the crosslinked solid-state ion-conductor in some examples, which consequently allows tuning of the ion conductivity. Tuning ion conductivity is also, for example, achievable by varying the amount of incorporated salt, which, in some examples influences the shape and extent of the phase separated regions and formed ion channels, and in some examples affects the glass transition.
An example process of manufacturing a crosslinked material, e.g. an ion-conductor is described in
An example process of manufacturing a polymerised material, e.g. an ion-conductor is described in
In examples, at least partially depositing a mixture on a substrate is achieved by casting the mixture, coating the mixture on the substrate, spin-casting or spin-coating; however other methods are envisaged. In some examples, before depositing the mixture by some techniques, such as solution deposition, the surface of the substrate is treated and/or cleaned. For example, the surface is cleaned by plasma cleaning. In some examples, the surface is chemically treated, for example to improve adhesion or introduce surface functionality. For some examples, cleaning of the surface improves the adhesion of the mixture to the substrate. In some examples the mixture comprises an adhesion additive which increases adhesion of the mixture to the surface, example adhesion additives are an acrylate when the surface is glass or a thiol when the surface is gold, other adhesion additives and surfaces are envisaged. In some examples the adhesion additive is bonded to the polymer, in other examples, the adhesion is not bonded to the polymer. The mixture is deposited in a thickness, for example, the mixture is deposited in a thickness from 50 nm to 5 mm.
Some examples comprise exposing the region of the mixture to radiation to cause the crosslinking. Examples of radiation include an electron beam and electromagnetic radiation. In examples, the mixture is selectively radiated by the use of a mask, such as a photolithographic mask, projector, and/or by modulating the source of radiation, such as by rastering a laser across the region of the mixture whilst selectively controlling the power of the laser. In some examples the resist mixture is heated or annealed to cause the crosslinking. In some examples this is achieved with thermal initiators, in other examples this is achieved without thermal initiators. In some examples where thermal initiators are not used, crosslinking is achieved at temperatures of 423 Kelvin and above. In some examples where thermal initiators are used, crosslinking is achieved at room temperature (298 Kelvin), in further examples where thermal initiators are used, this is achieved at a temperature between 323 Kelvin and 393 Kelvin. Some examples undergo heating at any point in manufacture which allows the facilitation of chemical reactions and/or the removal of volatiles from the crosslinked material.
In some examples, such as those of
Other techniques envisaged for providing the resist mixture on a substrate include for example drop casting, dip coating, spray coating, roll coating, painting, doctor blading, and imprint lithography.
An example process of manufacturing an ion-conductor is described in
It is to be appreciated that in some examples an additive of the resist mixture, such as a filler or dissolved substance, can be etched, extracted or removed from the crosslinked / polymerised mixture to increase porosity of the resulting material. The filler or dissolved substance can be developed then etched, or developed where the developer is the etchant. For example, a photoresist mixture containing a dispersion of poly(vinyl alcohol) nanoparticles can be spin-coated on a substrate, irradiated, and developed with isopropanol to remove non-crosslinked material, followed by the etchant water to remove poly(vinyl alcohol), thus leaving voids where the poly(vinyl alcohol) once resided.
An ion-conductor in accordance with examples described herein, e.g. comprising a crosslinked resist mixture and/or a polymerised resist mixture of examples described herein, is envisaged to have numerous uses. Hence in examples a device comprises the ion-conductor of examples described herein, such as an electrochemical, electromechanical, photoelectric, photonic, electrochromic, and/or electro-optic device. Such a device for example is, or comprises, a microchip assembly, a printed circuit board, a sensor, a battery, a photovoltaic cell, an electronic circuit, a microfluidic chip, an electronic component or another structure which relies on the flow of ions during its operation.
In some examples, such as those schematically illustrated by
The substrate comprises glass, quartz, sapphire, a ceramic, a metal, a polymer, carbon, or a photoresist, for example. In examples described herein, the substrate is for example part of a semiconductor microchip or wafer.
For examples of the crosslinked ion conductor described herein, direct current ion conductivity has been observed as up to 10-2 Siemens per centimetre (S/cm, equivalent to ×10-2 kg-1·m-3·s3·A2); however, higher values are envisaged. Typical values at 298 Kelvin are expected between 10-6 and 10-2 S/cm. A person skilled in the art will appreciate that the conductivity values obtained will depend on several variables, including the chosen composition of the crosslinked material ion-conductor, any chosen additives, and the temperature of operation.
It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the example, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2115612.0 | Oct 2021 | GB | national |
This application is a continuation under 35 U.S.C. § 120 of International Application No. PCT/EP2022/080231, filed Oct. 28, 2022, which claims priority to United Kingdom Application No. GB 2115612.0, filed Oct. 29, 2021, under 35 U.S.C. § 119(a). Each of the above-referenced patent applications is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/080231 | Oct 2022 | WO |
| Child | 18324825 | US |
