Patent Application
20220403499
The present invention concerns deposition of materials on a substrate. More particularly, but not exclusively, this invention concerns a method of depositing material on a substrate. The invention also concerns a method of determining optimum working distance and/or optimum working pressure for a remote plasma deposition system, a method of manufacturing a battery and a battery.
Deposition of materials using plasma deposition is well-known to those skilled in the art. Control of such deposition can, in certain circumstances, be difficult and the optimisation of deposition conditions is desirable to ensure that the material deposited on a substrate has the required properties and/or structure.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of depositing material.
The present disclosure relates to methods of depositing material by means of a plasma sputtering technique.
More specifically, the present disclosure relates to a method of depositing material by means of a plasma sputtering technique, wherein the plasma is generated remotely from the material to be sputtered.
In accordance with a first aspect of the present invention, there is provided a method of depositing a material on a substrate, the method comprising;
generating a plasma remote from a plasma target or targets suitable for plasma sputtering, wherein at least one distinct region of the target or targets comprises an alkali metal, alkaline earth metal, alkali metal containing compound, alkaline earth metal containing compound or a combination thereof.
exposing the plasma target or targets to the plasma, thereby sputtering material from the target or targets,
depositing the sputtered material on the substrate, the working distance between the target and the substrate being within +/−50% of the theoretical mean free path of the system.
Without wishing to be bound by theory, it is believed that the working distance has an influence on the “ad atom” energy of the sputtered material as it deposits onto the substrate. In a case where the working distance is greater than the mean free path of the system it is thought that it is more likely that an ion in the sputter flux would be involved in a collision before reaching the substrate, resulting in relatively low ad atom energy. Conversely, if the working distance is shorter than the mean free path of the system, the ad atom energy is relatively high.
A definition of the mean free path is the average distance between collisions for an ion in the plasma. The mean free path is calculated based on the volume of interaction (varied by the working distance), and the number of molecules per unit volume (varied by the working pressure).
The working distance is optionally from 50% of the theoretical mean free path of the system to 150% of the theoretical mean free path of the system, optionally from 70% of the theoretical mean free path of the system to 120% of the theoretical mean free path of the system and optionally from 80% of the theoretical mean free path of the system to 100% of the theoretical mean free path of the system.
The working distance is optionally at least 3.0 cm, optionally at least 4.0 cm optionally at least 5.0 cm, optionally at least 6.0 cm, optionally at least 7.0 cm, and optionally at least 8.0 cm. The working distance is optionally no more than 20 cm, optionally no more than 15 cm, optionally no more than 13 cm, optionally no more than 12.0 cm, optionally no more than 10.0 cm and optionally no more than 9.0 cm. The working distance between the target and the substrate is optionally from 3.0 cm to 20.0 cm, optionally from 4.0 cm to 15.0 cm, optionally from 5.0 cm to 13.0 cm, optionally from 6.0 cm to 12.0 cm, optionally from 7.0 cm to 10.0 cm, and optionally from 8.0 cm to 9.0 cm.
The working distance may be shorter than the mean free path of the sputtered material.
Without wishing to be bound by theory, at too short a working distance, the energy of the sputtered material may be so high as to deform or damage the substrate. A sputter flux with this much energy can also cause the formation of unfavourable high-energy oxide states due to plasma-induced induction in the sputter flux. Preferably, the working distance will be longer than a lower bound defined by when damage to the substrate, or/and formation of unfavourable oxide states is observed.
The working distance may be from 3.0 to 20.0 cm.
The working distance may be from 5.0 cm to 15 cm. Within this range, the material may be deposited with few undesirable oxide compounds forming in the film, and with the ad atom energy remaining relatively high.
The working distance may be from 6.0 cm to 14.0 cm. The working distance may be from 7.0 cm and 13.0 cm.
The working distance may be from 8.0 cm to 12 cm. Within this range, crystalline material forms with primary crystallite platelets, particularly for layered oxide materials
The working distance may be from 8.0 cm and 9.0 cm. Within this range, a higher proportion of the crystalline material is in a layered oxide structure.
The working pressure may be defined as the chamber pressure prior to the ignition of the remote plasma. The working pressure may be constant throughout the deposition process, or may fluctuate slights as targets are outgassed, or as targets age throughout deposition.
The applicant has discovered that it is possible to form crystalline films of materials directly onto substrates. In “directly”, what is meant is that the film forms a crystalline film with substantially no annealing step. This has been shown to be true, even for materials which form high energy crystal structures which would otherwise require an annealing step. The method has been shown to be effective on a wide range of substrate materials.
In a remote plasma system, the plasma is generated remotely from the plasma target(s). In conventional plasma deposition, it is the biasing of the target(s) which both produce and sustain the plasma. In a remote plasma deposition system, the plasma is generated elsewhere, and then directed to the targets by various electronic and or magnetic fields. The biasing of the target(s) allows for control of the rate of sputtering.
The deposited material may be crystalline. At least a portion of and optionally all of the deposited material may have a hexagonal crystal structure. At least a portion of and optionally all the deposited material may have a crystalline “layered oxide” structure. Such “layered oxide” structures are important when manufacturing solid-state batteries. A layered oxide structure allows for alkali metal ions to more easily de-intercalate from the crystal structure, resulting in a faster charging, higher capacity solid-state battery.
Layered oxide frameworks may generally be defined by the formula ABO2, where A is typically an alkali metal ion, alkaline earth metal ion or mixture, and B is typically one or more redox active transition metals, one or more transition metals or a mixture thereof. Elemental metals in the so called “post-transition metals” group such as aluminium, can also be incorporated into layered oxide frameworks.
The advantage of the formation of the crystalline material not requiring an annealing step is that a substrate of relatively low melting point may be used.
The substrate may comprise a polymer. The substrate may be flexible. The substrate may comprise polyethylene terephthalate (PET), or polyethylene naphthalate (PEN). PEN and PET are reasonably flexible, and relatively high tensile strength due to their semi-crystalline structure. The temperature of the substrate may not exceed 200 degrees at any point during the plasma deposition process.
The deposition may occur in a reactive atmosphere comprising oxygen.
The working pressure is optionally at least 0.0005 mBar, optionally at least 0.00065 mBar, optionally at least 0.0010 mBar, optionally at least 0.0020 mBar, optionally at least 0.0030 mBar, optionally at least 0.0040 mBar, and optionally at least 0.0045 mBar. The working pressure is optionally no more than 0.0100 mBar, optionally no more than 0.0090 mBar, optionally no more than 0.0080 mBar, optionally no more than 0.0070 mBar, and optionally no more than 0.0065 mBar. The working pressure is optionally from 0.0005 mBar to 0.0100 mBar, optionally from 0.0020 mBar to 0.0090 mBar, optionally from 0.0030 mBar to 0.0080 mBar, optionally from 0.0040 mBar to 0.0070 mBar, and optionally from 0.0045 mBar to 0.0065 mBar.
The working pressure may be from 0.0010 mBar to 0.0065 mBar. A higher working pressure in this range may result in a higher deposition rate. This is because a higher working pressure results in a larger number of process ion (usually Ar+) bombardments on the surface of the target, and hence material is sputtered from the target at a higher rate.
The crystallite size of the crystalline material that forms (the size of the crystallite platelets) may be from 8 to 65 nm when the working pressure is between 0.0010 mBar and 0.0065 mBar. Generally, larger crystallite sizes result in a higher proportion of the thin film being ordered material, as a lower percentage of the film is made up of disordered grain boundary material. This is important for thin-film batteries, as a larger crystallite size generally results in a thin-film battery with a higher usable capacity. A crystallite size within this range may be observed when the alkali metal containing material optionally comprises at least one of the following compounds (described here with non-specific stoichiometry): LiCoO, LiCoAlO, LiNiCoAlO, LiMnO, LiNiMnO, LiNiMnCoO, LiNiO and LiNiCoO.
When the working distance is from 8.0 to 9.0 cm, the range of crystallite sizes available may be narrower if a working pressure of from 0.0010 mBar to 0.0065 mBar is used. The crystallite size may be from 14 to 25 nm. This is evidence that within these parameter ranges, it is possible to form films with narrow and predictable thin film ranges. This may be important as it may allow deposition steps to be more predictable and repeatable at the industrial scale.
Without wishing to be bound by theory, it is thought that the layered oxide structure requires a high activation energy in order to form. The working pressure is directly related to the energy in the system. Therefore, there may exist a lower limit of working pressure, below which the desired layered oxide structure will not form. Preferably, the working pressure is above the lower bound defined by the pressure at which a desired layered oxide structure does not form, such that there is enough activation energy in the system for the desired layered oxide structure to form. For example, in the case where the alkali metal-containing compound is LiCoO2, a characteristic X-Ray diffraction peak of the layered oxide structure is shown at 19 degrees 2Theta (associated with the 003 plane). If the working pressure of the system is too low, a desired layered oxide structure may not form and this characteristic peak may not be present.
The working pressure may be at least 1.2e-3 mBar. Preferably, the working pressure is at least 4.6e-3 mBar.
At high working pressures, the energy in the system may be high, such that the substrate begins to be damaged. The damage may be caused by plasma induced temperature increases. Preferably, the working pressure is below an upper limit, wherein the upper limit is defined by the pressure at which observable damage is caused to the substrate. Preferably, the working pressure is below 0.0065 mBar.
The alkali metal, if present, may optionally be one or more of Li, Na, K, Cs and Rb, optionally one or more of Li, Na or K, optionally Li or Na and optionally Li. Lithium ions are sometimes used as conductive species in cathodes of solid state batteries. The alkaline earth metal, if present, may optionally be one or more of magnesium, calcium, strontium or barium, optionally one or more of magnesium, calcium and barium and optionally one or both of magnesium and calcium.
The one or more transition metal and/or one or more redox active transition metal may be in period 4 or period 5 of the Periodic Table. The statements below relate to transition metals that may or may not be redox active. At least one, and optionally each, transition metal may optionally be selected from the group consisting of Fe, Co, Mn, Ni, Ti, Nb and V.
The material deposited on the substrate may be of empirical formula AaM1bM2cO2, wherein A is an alkali metal (optionally lithium), M1 is one or more transition metal (optionally one or more of cobalt, nickel, niobium, vanadium and manganese) (b being the total of transition metal), M2 being aluminium, a being from 0.5 to 1.5 and z being from 0 to 0.5.
Optionally, a is 1, b is 1 and c is 0. Optionally, M1 is one of cobalt, nickel, vanadium, niobium and manganese.
Optionally, a is more than 1 and A is lithium. In the case, the materials are sometimes known as “lithium rich” materials. Such lithium-rich materials may be Li(4/3·2x/3)NixMn(2/3·x/3)O2 with x=0, 0.06, 0.12, 0.2, 0.3 and 0.4, for example.
Another such material is
wherein y has a value greater than 0.12 and equal to or less than 0.4.
Another such material is
wherein x has a value equal to or greater than 0.175 and equal to or less than 0.325; and y has a value equal to or greater than 0.05 and equal to or less than 0.35.
is another such material, wherein x is equal to or greater than 0 and equal to or less than 0.4; y is equal to or greater than 0.1 and equal to or less than 0.4; and z is equal to or greater than 0.02 and equal to or less than 0.3.
The alkali metal containing material may comprise lithium. The alkali containing metal may comprise at least one of the following compounds (described here with non-specific stoichiometry): LiCoO, LiCoAlO, LiNiCoAlO, LiMnO, LiNiMnO, LiNiMnCoO, LiNiO and LiNiCoO.
The method may comprise moving the substrate, and depositing sputtered material on the substrate, thereby forming material on the substrate. For example, if material was deposited on a first portion of the substrate, then the substrate may be moved, and material deposited on a second portion of the substrate.
This facilitates the reasonably rapid production of relatively large areas of material.
The substrate may comprise, or be in the form of, a sheet, optionally an elongate sheet. Such a sheet may be provided in the form of a roll or stack. Preferably, the substrate is provided as a roll. This facilitates simple and safe storage and handling of the substrate.
The substrate may be movably mounted to facilitate movement of the substrate (optionally in the form of a sheet). The substrate may be mounted in a roll-to-roll arrangement. Substrate upstream of the plasma deposition process is held on roller or drum. Substrate downstream of the plasma deposition process is held on a roller or drum. This facilitates simple and rapid handling of flexible sheets of substrate. A shutter may be provided to allow for a portion of the substrate to be exposed to the remotely generated plasma.
The use of a roll-to-roll arrangement has a number of advantages. It facilitates a high material throughput and allows a large material area to be deposited on one large substrate, though a series of depositions at a first portion of the substrate, followed by a second portion of the substrate, and so on. One of the main benefits of a roll-to-roll processing is that it allows for a number of depositions to occur without breaking vacuum. This saves both time and energy compared to systems in which the chamber needs to be taken to back up to atmospheric pressure from vacuum after deposition, in order to load a new substrate.
The upstream drum or roller for carrying the substrate may be located inside or outside the process chamber. The downstream drum or roller for carrying the substrate may be located inside or outside the chamber.
The substrate may be supplied in discrete sheets that are handled and stored in relatively flat sheets. The substrate may be planar in shape as the material is deposited thereon. This may be the case, when the substrate is provided in the form of discrete sheets, not being transferred to or from a roll. The sheets may each be mounted on a carrier, having greater structural rigidity. This may allow for thinner substrates to be used than in the case of substrate film held on a roller. It may be that the substrate is a sacrificial substrate. It may be that the substrate is removed before the layer(s) of material. Part or all of the substrate may be removed before integrating the crystalline layer or a part thereof in an electronic product package, component or other end product. For example, the layer of crystalline material may be lifted off from the substrate. There may be a layer of other intervening material between the base substrate and the crystalline material. This layer may lift off with the crystalline material or assist in the separation of the crystalline material from the base substrate. A laser-based lift-off technique may be used. The substrate may be removed by a process that utilises laser ablation.
Similar techniques are described in the prior art. For example, KR20130029488 describes a method of making a battery including using a sacrificial substrate and laser radiation to harvest a battery layer. In other examples, another suitable processing regime is used, provided it is capable of sufficiently high production throughput.
The substrate may optionally not exceed its temperature corrected yield strength at any point as it passes between the upstream and downstream rollers or drums. This is important as roll-to-roll processing machines require the substrate to be in tension as the substrate is fed through various rolls, rollers and drums. As the polymer heats up, its yield strength may begin to lower. If the polymer increases in temperature too much, the polymer may begin to deform as it passes through the roll-to-roll machine. This can lead to buckles, jams, and uneven deposition onto the substrate.
The temperature of the substrate during the deposition process is optionally no more than 500° C., optionally no more than 300° C., optionally no more than 200° C., optionally no more than 150° C., optionally no more than 120° C. and optionally no more than 100° C. The method of the present invention may take place at a low temperature, which facilitates the use of substrates and other materials which may not be usable at high temperatures. Furthermore, the handling of substrates at higher temperatures may be more difficult.
The maximum temperature reached at any given time by any given square of substrate material having an area of 1 cm2 as measured on the surface opposite to said surface on which the material is deposited and as averaged over a period of 1 second, may be no more than 500° C., optionally no more than 300° C., optionally no more than 200° C., optionally no more than 150° C., optionally no more than 120° C. and optionally no more than 100° C.
The thickness of the deposited alkali metal containing compound on completion of the method is optionally no more than 10 microns, optionally no more than 1.0 micron.
The thickness of the substrate is optionally no more than 1.6 microns. The thickness of the substrate provided is optionally less than 1.0 microns.
It is beneficial when designing solid state batteries for the substrate to be as thin as possible. This allows for batteries with a higher energy density to be manufactured. Preferably, if a thinner substrate became available, which met the necessary requirements of a relatively high temperature corrected yield strength and high degradation point, this substrate would be used for the method. In the case that the alkali metal containing compound is LiCoO2, the crystals are optionally aligned with the (101) and (110) planes substantially parallel to the substrate. This is beneficial as it means that the ion channels of the thin film are orientated perpendicular to the substrate, making for easier intercalation and de-intercalation of the ions from the battery. This improves the working capacity and the speed of charging of the battery.
The substrate optionally comprises a current collecting layer. The current collecting layer may comprise an inert metal. The current collecting layer may be platinum. The current collecting layer may be nickel. The current collecting layer may be gold. The current collecting layer may be platinum. The current collecting; layer may be aluminium. The current collecting layer may have a modified structure to increase its surface area. The current collecting layer may also act as an anode.
The deposition rate may be greater than 4 Ås-1. The deposition rate may be grater than 250 Ås-1. The deposition rate may be greater than 1000 Ås-1.
The method may comprises providing first and second targets. The target material of the first and second targets may optionally be different. The orientation of the first and second targets relative to the substrate may be mutually different.
The method may comprise exposing the first target to the plasma, and exposing the second target to the plasma, thereby sputtering material from the first and second targets. The substrate may be exposed to material sputtered from the first and second targets. The sputtering of material from the first target may generate a first plume corresponding to the trajectories of particles from the first target assembly onto the substrate. The sputtering of material from the second target may generate a second plume corresponding to the trajectories of particles from the second target assembly onto the substrate. The first and second plumes may converge at the substrate. The first and second targets may be configured such that more plasma energy may be received at one of the first and second targets than at the other of the first and second targets. This may be beneficial if the energy required to sputter the material of the first or second target is greater than the energy requires to sputter the material of the other of the first or second target. For example, if the first target comprises elemental lithium and the second target comprises cobalt, then the first and second targets may be configured such that the second target received more plasma energy than the first target because cobalt requires more energy than lithium to sputter from the target.
The method may comprise containing and shaping the plasma using magnetic and/or electrostatic fields so that the shape of the electron density distribution of the plasma is the same for any given cross-section taken across the majority of the width of the plasma within a margin of error. The margin of error may optionally be up to 30%, optionally up to 20%, optionally up to 10% and optionally up to 5%.
The shape of the electron density distribution of the plasma is optionally the same within a margin of error. This may be tested by means of visual inspection, with the visible glow being substantially the same along the width of the plasma. The plasma may be blanket-like. In this connection, the width and length of the visible plasma cloud may each be at least five times greater than the thickness. The generation of the plasma may be performed by at least one antenna extending in a direction parallel to the width of the substrate. The generation of the plasma may be performed using a pair of antennae on opposing sides of plasma separated by distance L, each antenna having length, W. The thickness of plasma (defined either by maximum extent of glow in visible spectrum or the largest distance as measured in the direction perpendicular to both L and W which covers 90% of the free electrons in the plasma).
The first or second target may be closer to the plasma than the other of the first and second target. Such an arrangement may facilitate the first or second target receiving more plasma energy than the other of the first and second target.
The first or second target may, for any given cross-section section taken across the majority of the width of the plasma, be angled differently to the horizontal than the other of the first and second target. Such an arrangement may facilitate the first or second target receiving more plasma energy than the other of the first and second target.
One or both of the first and second target may be planar.
The target(s) of the second target assembly present, for any given cross-section section taken across the majority of the width of the plasma, present substantially the same amount of material to the plasma as the target(s) of the first target assembly.
The one or more targets is optionally opposite the substrate. Such an arrangement is effective when the plasma is generated remotely.
The surface onto which the material is deposited may have a surface roughness XS or less, where XS=100 nm, and the layer so desposited may have a thickness of from 0.01 to 10 μm and a surface roughness of no more than X1, where X1 equals the product of F and XS, where F is a factor in the range of 1 to 2.
XS may be no more than 10% of the thickness of the substrate. The product of the thickness of the substrate and XS may be no more than 105 nm2.
The substrate, optionally a polymer substrate, may be provided with embedded particles and of all of the embedded particles within or on the polymer material, the majority of those that contribute to surface roughness of the substrate have a median size from 10% to 125% of Xs.
Alternatively, the substrate, optionally a polymer substrate, may be provided with embedded particles and of all of the embedded particles within or on the polymer material, the majority of those that contribute to surface roughness of the substrate have a median size of no less than 150% of Xs.
The method may include a step of depositing material onto the surface using sputter deposition to form a further layer having a thickness of from 0.01 to 10 μm and a surface roughness of no more than 150% of XS, the material composition of the crystalline layer being different from the material composition of the further layer.
The method may comprise plasma sputtering material from a first target comprising an alkali metal or an alkaline earth metal onto a surface of or supported by a substrate, there being at least a first plume corresponding to trajectories of particles from the first target onto the surface, and plasma sputtering material from a second target comprising a transition metal (such as cobalt) onto the surface, there being at least a second plume corresponding to trajectories of particles from the second target onto the surface, and wherein the first target is positioned to be non-parallel with the second target, the first plume and the second plume converge at a region proximate to the surface of or supported by the substrate, and an optionally crystalline layer is formed on the surface at said region.
More plasma energy may be received at the first target than at the second target. The first target may face towards the substrate in a first direction, and the second target may face towards the substrate in a second direction, the first and second directions converging towards the substrate.
The notional line parallel to the first direction which extends from the centre of the surface of the first target may intersect, in the cross-section, the notional line parallel to the second direction which extends from the centre of the surface of the second target, at a location closer to the substrate than to either of the targets. The location of the intersection may be closer to the substrate than half of the shortest distance from either of the targets to the substrate.
At least one of the substrate and the first and second targets may be moving as an optionally crystalline layer is being formed on the surface.
The substrate may have a radius of curvature at the region at which the first plume and the second plume converge and the targets are arranged circumferentially around the centre of the radius of curvature.
According to a second aspect of the present invention, there is provided a method of determining an optimum working distance for a remote plasma deposition system configured for the deposition of layered oxide materials, wherein the method comprises:
selecting a range of working distances, such that the theoretical mean free path of the system falls within said range,
for a number of test specimens, for each respective specimen, performing the method according to the first aspect of the invention at different working distances within the selected range,
performing X-Ray diffraction on each of the test specimens after deposition has occurred,
identifying specimens where a diffraction peak characteristic of a layered oxide structure is present,
from those specimens, selecting the specimen wherein the (normalised) intensity of said characteristic peak is highest, and subsequently selecting the working distance for the system to that which was used during deposition of said test specimen.
The test specimens of the method may optionally be replaced with an average value for a number of test specimens, comprising a number of test specimens wherein the method of the first aspect of the invention has been performed a number of times at the same working distance, and an average taken. The method may also comprise any standard error analysis techniques known to the person skilled in the art.
The method may optionally be performed a number of times such that a range of optimal working distances can be found for operating the system.
According to a third aspect of the present invention, there is provided a method of determining an optimum range of working pressures for a remote plasma deposition system configured for the deposition of layered oxide materials, wherein the method comprises:
selecting an initial range of working pressures, from 0.00065 mBar to 0.01 mBar (optionally between 0.001 mBar and 0.007 mBar),
for a number of test specimens, for each respective specimen, performing the method according to the first aspect of the invention at different working pressures within the selected range,
performing X-Ray diffraction on each of the test specimens after deposition has occurred,
selecting the test specimen which was deposited at the lowest working pressure from the group of test specimens which display a characteristic X-Ray diffraction peak of a layered oxide material, and setting this working pressure as the lower bound of the range,
selecting the test specimen which was deposited at the highest working pressure from the group of test specimens which do not show observable signs of damage to the substrate, and setting this working pressure as the higher bound of the range.
The initial range of working pressures may be chosen in accordance with the choice of working pressure described above in relation to the method of the present invention. The test specimens of the method may optionally be replaced with an average value for a number of test specimens, comprising a number of test specimens wherein the method of the first aspect of the invention has been performed a number of times at the same working pressure, and an average taken. The method may also comprise any standard error analysis techniques known to the person skilled in the art.
The method may further comprise selecting the optimum working pressure of the system within the desired range. The optimum working pressure may be the working pressure within the range which results in the highest deposition rate.
It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings which can be briefly summarised as follows.
The crystalline material in this example takes the form ABO2. In the present example, the ABO2 material takes a layered oxide structure. In the present example, the ABO2 material is LiCoO2. However, the method of the present example has been shown to work on a wide range of ABO2 materials. In other examples, the ABO2 material structure comprises at least one of the following compounds (described here with non-specific stoichiometry): LiCoO, LiCoAlO, LiNiCoAlO, LiMnO, LiNiMnO, LiNiMnCoO, LiNiO and LiNiCoO. These materials are potential candidates for manufacturing a battery cathode. Those skilled in the art will realise that the stoichiometry may be varied.
In this example, the ABO2 material is LiCoO2 and is deposited as a layer that is approximately 1 micron thick. In other examples, the ABO2 material is deposited as layer that is approximately 5 microns thick. In yet further examples, the ABO2 material is deposited as a layer that is approximately 10 microns thick. With reference to
In this example, the target 104 comprises material LiCoO2. Briefly, the chamber 122 is evacuated until a sufficiently low pressure is reached. Power provided by power supply 112 is used to power the remote plasma generator 106 to generate a plasma. Power is applied to the target 104 such that plasma interacts with target 104, causing LiCoO2 to be sputtered from the target 104 and onto the substrate 128. In the present example, the substrate 128 comprises a polymer sheet which is introduced into the housing 114 via inlet 130 and out of the housing 114 via outlet 132. A powered roller 134 is used to help move the substrate 128. The LiCoO2 is deposited onto the substrate 128 as a crystalline (non-amorphous) material.
The apparatus 100 also comprises a shutter 136, for restricting deposition of sputtered material onto the substrate 128, and an input 138 for cooling the drum. Shutter 136 allows a portion of the substrate 128 to be exposed to the sputtered material.
As mentioned above, a powered roller 134 is used to help move the substrate 128 into and out of the plasma deposition apparatus 100. Powered roller 134 is part of a roll-to-roll substrate handling apparatus (not shown) which comprises at least a first storage roller upstream of the plasma deposition apparatus 100 and a second storage roller downstream of the plasma deposition apparatus 100. The roll-to-roll substrate handling apparatus is a convenient way of handling, storing and moving thin, flexible substrates such as the polymer substrate used in this example. Such a roll-to-roll system has a number of other advantages. It allows for a high material throughput and allows a large cathode area to be deposited on one substrate, throughout a series of depositions at a first portion of the substrate, followed by a second portion of the substrate, and so on. Furthermore, such roll-to-roll processing allows for a number of depositions to occur without breaking vacuum. This saves both time and energy compared to systems in which the chamber needs to be taken back up to atmospheric pressure from vacuum after deposition in order to load a new substrate. In other examples, sheet-to-sheet processing is used instead of roll-to-roll processing, wherein the substrate is provided with a support. Alternatively, the substrate may be supplied in discrete sheets that are handled and stored in relatively flat sheets. The substrate may be planar in shape as the material is deposited thereon. This may be the case, when the substrate is provided in the form of discrete sheets, not being transferred to or from a roll. The sheets may each be mounted on a carrier, having greater structural rigidity. This may allow for thinner substrates to be used than in the case of substrate film held on a roller. It may be that the substrate is a sacrificial substrate. It may be that the substrate is removed before the layer(s) of material. Part or all of the substrate may be removed before integrating the crystalline layer or a part thereof in an electronic product package, component or other end product. For example, the layer of crystalline material may be lifted off from the substrate. There may be a layer of other intervening material between the base substrate and the crystalline material. This layer may lift off with the crystalline material or assist in the separation of the crystalline material from the base substrate. A laser-based lift-off technique may be used. The substrate may be removed by a process that utilises laser ablation.
Similar techniques are described in the prior art. For example, KR20130029488 describes a method of making a battery including using a sacrificial substrate and laser radiation to harvest a battery layer. In other examples, another suitable processing regime is used, provided it is capable of sufficiently high production throughput.
The polymer substrate 128 is under tension when moving through the system, for example withstanding a tension of at least 0.001N during at least part of the processing. The polymer is robust enough such that when the polymer is fed through the roll-to-roll machine, it does not experience deformation under tensile stress. In this example, the polymer is Polyethylene terephthalate (PET), and the substrate 128 has a thickness of 1 micron or less, in examples the thickness is 0.9 microns. The substrate 128 is pre-coated with a current collecting layer, which is made of an inert metal. In this example, the inert metal used as the current collecting layer is platinum. The yield strength of the PET film is sufficiently strong that the substrate does not yield or plastically deform under the stresses of the roll-to-roll handling apparatus. The inert metal used in other examples can alternatively be gold, iridium, copper, aluminium or nickel. The use of such thin polymer substrates is beneficial because this facilitates batteries with a higher energy density to be manufactured. In other examples, a material, which is not polymeric, is used, providing that it can be manufactured in a sufficiently thin and flexible manner to allow for a high battery density and ease of handling post-deposition.
The plasma deposition process and subsequent manufacturing processes are however subject to the technical challenges that working with such thin layers impose.
Before the substrate 128 is so pre-coated, it has a surface roughness that is carefully engineered so as (a) to be great enough to mitigate the undesirable effects that would otherwise result from electrostatic forces (such as increasing the force required to unwind the polymer film from the drum on which it is held) and (b) to be small enough that the roughness does not cause problems when depositing material onto the substrate. In this example, the surface roughness is engineered to be about 50 nm. It will be noted that the product of the thickness of the substrate (0.9 microns) and the surface roughness is 4.5×104 nm2 and is therefore less than 105 nm2 and less than 5×104 nm2 in this example. It has been found that that the roughness needed for easing handling of thin films rises with decreasing thickness. Generally, it has been found that the roughness required to improve handling of thinner substrates (i.e. less than 10 microns, particularly less than 1 micron) increases as the substrate thickness decreases.
Examples such as those of
The roughness of the substrate can be measured with a profilometer. This instrument has a stationary stylus. The surface to be measured is translated under the stylus, and the deflections of the stylus measure the surface profile, from which various roughness parameters are calculated.
Roughness can also be measured using “non-contact” methods. A suitable machine for measuring roughness is the “Omniscan MicroXAM 5000B 3d” which uses optical phase shift interference to measure the surface profile.
The roughness, Ra, can be calculated using the formula
where the deviation y from a smooth surface is measured for n data points. The surface roughness, Sa, of an area A extending in the x- and y-directions can be calculated using the formula:
where Z is the deviation from a mathematically perfectly smooth surface.
In the present example, the average surface roughness is measured with a non-contact method.
The remotely generated plasma is created by the power supplied to the antennae 116 by power supply 112. There is therefore a measurable power associated with that used to generate the plasma. The plasma is accelerated to the target by means of electrically biasing the target 104, there being an associated electrical current as a result. There is thus a power associated with the bias on the target 104. In this example, the ratio of the power used to generate the plasma to the power associated with the bias on the target is greater than 1:1, and optionally greater than 1.0:1.0. Note that in this example, the ratio is calculated on the assumption that the power efficiency of the plasma-generating source is taken to be 50%. The power associated with the bias on the target is at least 1 Wcm−2. In further examples, the ratio of the power used to generate the plasma to the power associated with the bias on the target is greater than 1:1, and no more than 7:2, optionally 7.0:2.0. In yet further examples, the power associated with the bias on the target is greater than 1:1 and no more than 3:2, optionally 3.0:2.0. In some examples, the power efficiency of the plasma generating source is taken to be 80%. In some examples, the power associated with the bias on the target is 10 Wcm−2. In yet further examples, the power associated with the bias on the target is 100 Wcm−2. In yet further examples, the power associated with the bias on the target is 800 Wcm−2. In other examples, the efficiency of the plasma generating source may be different, and the power ratio may also be different.
When the LiCoO2 film is deposited onto the substrate, it forms a crystalline film of LiCoO2. The crystalline structure which forms onto the substrate is in the R
Throughout the plasma deposition process, the temperature of the substrate 128 does not exceed the degradation point of the polymer substrate 128. Moreover, the temperature of the substrate is sufficiently low throughout the deposition process such that the temperature adjusted yield stress of the polymer substrate remains sufficiently high such that the polymer substrate does not deform under the stresses exerted by the roll-to-roll processing machine.
The general shape of the confined plasma made from the remote plasma generator 106 is shown by the dashed lines B in
In addition the means 112 of powering the plasma source, may be of RF, (Direct Current) DC, or pulsed-DC type.
In this first example, the target assembly 102 comprises only one target 104. This target is made of LiCoO2. It should be appreciated that alternative and/or multiple target assemblies may be used, for example, comprising a distinct region of elemental lithium, a distinct region of elemental cobalt, a distinct region of lithium oxide, a distinct region of cobalt oxide, a distinct region of a LiCo alloy, a distinct region of LiCoO2, or any combination thereof. In other examples, the ABO2 material may not be LiCoO2. In these examples, the target assembly or assemblies contain distinct regions of A, distinct regions of B, distinct regions of a compound containing A and/or B, and/or distinct regions containing ABO2
For the avoidance of doubt, the target 104 of the target assembly 103 acts as a source of material alone and does not function as a cathode when power is applied to it from the RF, DC or pulsed DC power supply.
In this example, the working pressure of the system is 0.0050 mBar. The theoretical mean free path of the system is approximately 10 cm. The theoretical mean free path is the average distance between collisions for an ion in the plasma. The working distance between the target 104 and substrate 128 is approximately 8.5 cm. This working distance is therefore approximately 85% of the theoretical mean free path of the system.
In this example, the working pressure is above a lower bound below which crystalline material in the layered oxide structure does not form, but below an upper bound above which observable damage is caused to the substrate. The working distance is shorter than an upper bound above which crystalline material in the layered oxide structure does not form, and longer than a lower bound below which the energy of the deposition causes observable damage to the substrate, or unfavourable oxide states to form.
The average crystallite size of the crystallites which form on the film in this example is around 20 nm. In other examples, the average crystallite size of the crystallites which form on the film is around 50 nm.
In an alternative example, the working pressure of the system is 0.0020 mBar. The theoretical mean free path of the system is approximately 12 cm. The working distance between the target 104 and substrate 128 is approximately 9 cm. This working distance is therefore approximately 75% of the theoretical mean free path of the system.
In an alternative example, the working pressure of the system is 0.0065 mBar. The theoretical mean free path of the system is approximately 15 cm. The working distance between the target 104 and substrate 128 is approximately 7.5 cm. This working distance is therefore approximately 50% of the theoretical mean free path of the system.
A second example method uses the apparatus shown in
Table 1 shows the properties of the resultant exemplary battery cathodes produced in accordance with the second example:
In Table 1 above, the elemental film composition was determined by x-ray photoelectron spectroscopy using a Themo Fisher K-alpha spectrometer with a MAGCIS ion gun. Quoted compositions were taken from depth profiling measuring at about 10 levels with a film. Plasma source power is the electrical power supplied to generate the plasma. Sputtering power is the electrical power applied to the target 204. Process pressure is the pressure in the chamber. Film thickness and roughness measurements were taken after deposition, using an Omniscan MicroXAM 5000b 3d optical profiler. Film thicknesses were measured after deposition, as step-heights at masked edges and roughness measurements were taken from sample areas of about 400 microns×500 microns.
The absence of extra reflections associated with the Fd3m space group is an initial indicator that the LiCoO2 deposited is in the R
Also notably absent is the peak associated with the (003) plane. This implies that very few crystals are orientated in such a way that the (003) plane is parallel to the substrate surface. It is beneficial that very few crystals are orientated in this way. A detailed explanation is beyond the scope of the present application, but briefly, the accessible capacity of a cathode increases when a higher proportion of the crystals are aligned such that the (101) and (110) planes are parallel to the substrate, as opposed to being aligned such that the (003) plane is parallel to the substrate as the apparent resistance to ion migration is lower. The crystals have formed such that the longitudinal axis of the crystals is normal to the substrate. In other words, the crystals have formed in an epitaxial manner The applicant has discovered that if the ratio of the power used to generate the plasma to the power associated with the biasing of the target is more than 1:1, then generally a crystalline material is deposited. In Sample 1, the ratio is 1800:500 (3.6:1) and in Sample 2, the ratio is 1800:800 (9:4). Note that in this example, the ratio is calculated on the assumption that the power efficiency of the plasma-generating source is taken to be 50%.
In a comparative example, the experiment was repeated with a plasma source power of 1 kW and a power associated with bias to the target of 1 kW. The material deposited was substantially amorphous. The performance of the film of the comparative example as a cathode was investigated by depositing an electrolyte (in this case, LiPON) and an anode metal on top of the cathode layer, thereby making a solid state battery. The charge-discharge characteristics of the battery were investigated and were found to be poor, with a cathode specific capacity of about 10 mAh/g. When analogous batteries were made using crystalline LiCoO2 such as that formed in Sample 1 and Sample 2, the charge-discharge characteristics were far superior, with typical cathode specific capacities of about 120 mAh/g.
A plasma of argon ions and electrons is generated by means of two electrically powered spaced apart antennae 316. The plasma is confined and focused by a magnetic field controlled by two pairs of electromagnets 308, each pair being positioned proximate to one of the antennae 316 and the electric field generated by the system. The overall shape of the plasma (the 90% highest concentration of which being illustrated in highly schematic fashion in
The plasma source is spaced apart from the targets, and may thus be considered as a remotely generated plasma. The theoretical mean free path of the system (that is, the average distance between collisions for an ion in the plasma) is about 12 cm, meaning that the majority of particles travel from the target to the substrate without colliding with any argon ions in the plasma.
The amount of oxygen introduced into the chamber may be reduced in some other examples if distinct regions of lithium oxide and cobalt oxide are present in targets 304, 303, and the oxygen content in such targets may be sufficiently high in some examples such that no additional oxygen gas need be introduced into the chamber 322 at all.
It will be seen that in
In performance of the method, the plasma generated is used to sputter material from the first target and from the second targets onto the substrate.
As shown in
An example of a battery cathode made in accordance with the second example will now be described with reference to
As shown on the Scanning Electron Microscope (SEM) image of
A method of making a cathodic half-cell in accordance with a fifth example will now be described with reference to
In this example, the LiPON is deposited in substantially the same way as the ABO2 materials in the first, second, third or fourth examples, using a remotely-generated plasma. However, in this example, the target material used is Li3PO4, with deposition occurring in a reactive nitrogen atmosphere. In other examples, the target assembly may include a number of targets, with distinct regions of lithium and/or phosphorous containing compounds, elemental lithium, or lithium oxide. In other examples, the deposition additionally occurs in a reactive oxygen atmosphere.
An example of a method of making a solid-state battery cell in accordance with a sixth example will now be described with reference to
An example of a method of making a solid-state battery in accordance with a seventh example will now be described with reference to
Alternatively, in other examples the current collector material acts as an anode material. Alternatively, in a second sample of the seventh example of the invention a further anode material may be deposited. This is shown schematically in
An example of a method of determining an optimum working distance for a remote plasma deposition system configured for the deposition of layered oxide materials in accordance with an eighth example will now be described with reference to
In this eighth example, the characterisation technique used is X-ray diffraction, and the characteristic property is a diffraction peak or series of diffraction peaks.
In some examples, the test specimens of the method are replaced with an average value for a number of test specimens, comprising a number of test specimens, wherein the method of the first example has been performed a number of times at the same working distance, and an average taken. In some examples the method may be performed a number of times such that a range of optimal working distances can be found for operating the system.
An example of a method of determining an optimum range of working pressures for a remote plasma deposition system configured for the deposition of layered oxide materials in accordance with a ninth example will now be described with reference to
In this ninth example, the characterisation technique used is X-ray diffraction, and the characteristic feature is a feature comprises a characteristic X-Ray diffraction peak of a layered oxide material.
In further examples, the test specimens of the method are replaced with an average value for a number of test specimens, comprising a number of test specimens wherein the method of the first example has been performed a number of times at the same working pressure, and an average taken.
In some examples, the method also comprises selecting the optimum working pressure of the system within the desired range. In this example, the optimum working pressure is the working pressure within the range that results in the highest deposition rate.
An example of a method of determining the crystallite size for deposition of layered oxide materials in accordance with a tenth example will now be described with reference to
The selected range of working pressures may be from 0.001 to 0.007 mBar, for example.
It is beneficial to have a narrow distribution of crystallite sizes, as this makes the crystallite size of films deposited on an industrial scale both predictable and repeatable.
An example of a method of depositing a material on a substrate in accordance with an eleventh example of an example will now be described with reference to
The method of depositing material on a substrate as described by the eleventh example comprises all of the features of the deposition of the first example, although in this example, the target material may be any material. In this example, the target material is crystalline, however in other examples the deposited material may take a semi-crystalline form, or be amorphous.
Also presented is a twelfth example, which relates to a method of manufacturing a component for an electronic device comprising a substrate, which will now be described with reference to
In this example, the substrate comprises one intermediate layer, which may optionally act as a current collecting layer. In other examples, there are more intermediate layers, which help with adhesion during deposition steps. In some other examples, there is no intermediate layer. The deposition of the intermediate layer onto the substrate is be performed in accordance with the method as described in the eleventh example. In other examples, deposition of the intermediate layer onto the substrate is performed by another appropriate deposition technology such as sputtering, thermal evaporation, electron beam evaporation, pulsed laser deposition, or other thin film deposition technology.
In this example, the method comprises depositing a first semiconducting layer of material. In this example, the first semiconducting layer is deposited onto an intermediate layer of material. In other examples, the first semiconducting layer is deposited directly onto the substrate. In this example, the first semiconducting layer comprises silicon. In other examples, the first semiconducting layer comprises aluminium, and in some further examples, gallium nitride. In examples where the semiconducting layer of material is gallium nitride, the deposition occurs under a reactive nitrogen atmosphere. In this example, the first semiconducting layer of material is doped n-type. This is achieved in this example by sputtering of a target comprising a compound containing phosphorous. In other examples, this is achieved by use of a different dopant such as arsenic, antimony, bismuth or lithium. In some further examples, the semiconducting layer of material is doped p-type, with dopants such as boron, aluminium, gallium or indium. In further examples, the semiconducting layer of material is not doped, and is an intrinsic semi-conductor. In some of these examples, the dopant material is not introduced as a target which can be sputtered, and is instead introduced as a gas after deposition, such that the dopant diffuses into the surface of the semiconducting layer.
In this example, the method comprises depositing a second semiconducting layer of material, onto the first semiconducting layer of material. In other examples, the second semi-conducting layer of material is deposited directly onto the substrate or the intermediate layer (if present). In this example, the second semiconducting layer of material is an intrinsic semiconductor. In this example, the second semiconducting layer of material is gallium nitride. In further examples, the second semiconducting layer of material is doped n-type with dopants such as phosphorous, arsenic, antimony, bismuth or lithium. In some further examples, the second semiconducting layer of material is doped p-type, with dopants such as boron, aluminium, gallium or indium. In some of these examples, the dopant material is not introduced as a target that can be sputtered, and is instead introduced as a gas after deposition, such that the dopant diffuses into the surface of the semiconducting layer.
In this example, the method comprises depositing a third semiconducting layer of material. In this example, the third semiconducting layer is deposited onto the second semi-conducting layer of material. In other examples, the third semiconducting layer is deposited directly onto the first semiconducting layer, second semiconducting layer, the intermediate layer or the substrate. In this example, the third semiconducting layer comprises silicon. In other examples, the third semiconducting layer comprises aluminium, and in some further examples, gallium nitride. In some examples where the semiconducting layer of material is gallium nitride, the deposition occurs under a reactive nitrogen atmosphere. In this example, the third semiconducting layer of material is doped p-type. This is achieved in this example by sputtering of a target comprising a compound containing boron. In other examples, this is achieved by use of a different dopant such as aluminium, gallium or indium. In some further examples, the third semiconducting layer of material is doped n-type, with dopants such as phosphorus, arsenic, antimony, bismuth or lithium. In further examples, the third semiconducting layer of material is not doped, and is an intrinsic semi-conductor. In some of these examples, the dopant material is not introduced as a target, which can be sputtered, and is instead introduced as a gas after deposition, such that the dopant diffuses into the surface of the semiconducting layer.
The method of this example may therefore be used to form a p-n or p-i-n junction.
In this example, no further dopants are introduced into some of the semiconducting layers hitherto described. In some examples, germanium is introduced as a dopant in the first, second and/or third layers. Germanium alters the band gap of the electronic device, and improves the mechanical properties of each semiconducting layer of material. In some examples, nitrogen is introduced as a dopant in the first, second and/or third layers of material. Nitrogen is used to improve the mechanical properties of the semiconducting layers formed.
Also presented is a thirteenth example, which relates to a method of manufacturing a crystalline layer of Yttrium Aluminium Garnet (YAG), which will now be described with reference to
In this example, the dopant material is a lanthanide.
In this example, the dopant material comprises neodymium. In other examples, the dopant material comprises chromium or cerium in addition to neodymium. In this example, the crystalline layer of material comprises 1.0 molar percent neodymium. In some examples, the material also comprises 0.5 molar percent cerium.
In yet further examples, the dopant material comprises erbium. In this example, the dopant material is provided as a target, and sputtered as described in the eleventh example. The crystalline layer of material in this further example comprises 40 molar percent erbium. In one example, the crystalline layer of material comprises 55 percent erbium.
In yet further examples, the dopant material comprises ytterbium. In one of these examples, the crystalline layer of material comprises 15 molar percent ytterbium.
In yet further examples, the dopant material comprises thulium. In further examples, the dopant material comprises dysprosium. In further examples, the dopant material comprises samarium. In further examples, the dopant material comprises terbium.
In yet further examples, the dopant material comprises cerium. In some examples where the dopant material comprises cerium, the dopant material also comprises gadolinium.
In some examples, instead of the dopant material being provided as a distinct region of a target or targets, the dopant material is, at least in part, introduced after the deposition of the layer of crystalline material, by providing the dopant material as a gas, such that it diffuses into the layer of crystalline material. According to a fourteenth example, a method of manufacturing a light emitting diode is presented, which will now be described with reference to
The methods according to the twelfth and thirteenth examples may be performed inside the same process chamber.
According to a fifteenth example, a method of manufacturing a permanent magnet is presented, which will now be described with reference to
In this example, the final layer of material comprises 6.0 molar percent dysprosium. In further examples, the molar percentage of dysprosium is less than 6.0.
The high target utilisation that the current method provides is beneficial when constructing electronic devices from rare elements such as dysprosium.
Dysprosium is available in limited Earth abundancy, and so a deposition system with a high target utilisation results in less material waste.
According to a sixteenth example, a method of manufacturing a layer of Indium Tin Oxide (ITO) is presented, which will now be described with reference to
In yet further examples the targets may comprise an oxide of indium, or an oxide of tin. The deposition process in further examples comprises providing oxygen, such that the sputtered material from the targets reacts with the oxygen in order to form Indium Tin Oxide on the substrate.
According to a seventeenth example, not separately illustrated, a method of manufacturing a photovoltaic cell is presented. In this example, the method further comprises the deposition of an ITO, as described in the fifteenth example. In further examples, no layer of ITO is deposited. In this example, the method also comprises the deposition of a layer of perovskite material in between a n-type doped layer of semiconducting material and a p-type doped layer of semiconducting material. The perovskite layer of material is in this case deposited as described by the method of the eleventh example. In further examples, it is deposited by another suitable means such as physical vapour deposition, or wet chemistry techniques. In further examples, no perovskite layer of material is deposited.
In alternative examples, the method comprises the deposition of a layer of copper indium gallium selenide in accordance with the eleventh example. The copper, indium, gallium, and selenide is provided as distinct regions of the target or targets. In this example the copper is provided as an elemental target, and the indium, gallium, and selenide are provided as oxide targets. Other combinations of oxide, elemental, compound or composite targets are used in further examples. The number of targets used thus may differ in further examples, and a single target may be used.
In some examples, the method comprises the deposition of a layer of cadmium sulphide in accordance with the eleventh example. In this example, the cadmium and sulphide are provided as distinct regions of the targets in oxide form. Other combinations of oxide, elemental, compound or composite targets are used in further examples. The number of targets used thus may differ in further examples, and a single target may be used.
In some examples, the method comprises deposition of a layer of cadmium telluride in accordance with the eleventh example. The cadmium and telluride is provided as distinct regions of elemental targets in tis example. In other examples, the cadmium and telluride is provided as distinct regions of the target or targets in elemental, an oxide, a composite or any combination thereof. The number of targets used thus may differ in further examples, and a single target may be used.
Whilst the forgoing description has been described and illustrated with reference to particular examples, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.
Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the example, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1916633.9 | Nov 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/052894 | 11/13/2020 | WO |
