Patent Description:
Graphene is a substance composed of carbon atoms forming a crystal lattice one atom in thickness. Various applications have been proposed for graphene, including its use in radio-frequency transistors and for forming transparent highly conductive and flexible electrodes, such as for displays. It is of particular benefit in applications where high mobility conductors are desired. Most applications of graphene require a macroscale-sized graphene layer, comprising one or a few layers of carbon atoms, which is transferred onto a substrate of a material selected based on the particular application.

Graphene is generally formed using a chemical vapor deposition (CVD) process, wherein graphene is deposited over a base substrate such as a copper foil. However, a difficulty is that it is relatively difficult to remove the graphene layer from the base substrate without damaging or polluting the graphene layer and/or degrading its conductivity.

Furthermore, in some embodiments it would be desirable to provide a method of forming a three-dimensional (3D) graphene device.

There is thus a need in the art for an improved method of forming a graphene device, and to one or more graphene devices formed based on such a method.

It is an aim of embodiments of the present disclosure to at least partially address one or more needs in the prior art.

According to one aspect, there is provided a method of forming a graphene device, wherein a polymer material from the n-xylylene family forms the support of said graphene film, the method comprising:.

According to one embodiment, the polymer material comprises parylene.

According to one embodiment, the graphene film is formed over a three-dimensional surface of the substrate.

According to one embodiment, removing the substrate from the graphene film is performed by a process of electrochemical delamination or using an acid etch.

The method may be for forming a sensor device to be placed over a three-dimensional form, wherein: the substrate on which the graphene film is formed comprises a mold having the shape of the three-dimensional form.

The mold may be formed of a first material and at least one zone of a second material; during the formation of the graphene film, graphene selectively forms on the at least one zone of the second material and not on
the first material; and the polymer material is deposited over the graphene film and at least a portion of the first material.

The method may further comprise, after removing the substrate from the graphene film, performing a further gas phase deposition of the polymer material to encapsulate the graphene film.

The graphene film may be deposited to form a conductive track having a meandering form in a detection zone.

The graphene film may be deposited in the form of a first plate of graphene formed in a detection zone and connected to a first conductive track, and the method further comprises: forming a further graphene film covered by a further deposition of polymer material, wherein the further graphene film is deposited in the form of a second plate of graphene; and assembling the first and second graphene films such that the first and second graphene plates form a capacitive interface in the detection zone separated by a layer of the polymer material.

According to a further aspect, there is disclosed a sensor device comprising: a graphene film covered on at least one side by a polymer material having, on a portion of its inside surface, a detection element formed of a graphene film, the polymer material contacting with and supporting the graphene film.

The disclosed detection element may comprise a meandering conductive track formed in a detection zone and electrically connecting a first conductive track to a second conductive track.

The disclosed detection element may comprise first and second graphene plates at least partially overlapping each other, the first graphene plate being connected to a first conductive track, and the second graphene plate being connected to a second conductive track.

The disclosed graphene device may further comprise a detection circuit coupled to the first and second conductive tracks.

The foregoing and other features and advantages will become apparent from the following detailed description of embodiments, given by way of illustration and not limitation with reference to the accompanying drawings, in which:.

For ease of illustration, the various figures are not drawn to scale.

Throughout the present description, the term "connected" is used to designate a direct electrical connection between two elements, whereas the term "coupled" is used to designate an electrical connection between two elements that may be direct, or may be via one or more other components such as resistors, capacitors or transistors. Furthermore, as used herein, the term "substantially" is used to designate a range of +/- <NUM> percent of the value in question.

<FIG> is a cross-section view of a graphene device comprising a film <NUM> of graphene, which is for example just one atom in thickness, or may have a thickness of up to <NUM> atom layers, depending on the application and the desired electrical conductivity. In particular, the graphene film <NUM> is for example formed of a plurality of graphene mono-layers attached together. In some embodiments, the graphene film <NUM> is doped in order to reduce its surface resistance, for example using P-dopants such as AuCl3 and/or HN03. Additionally or alternatively, layers of one or more dopants such as FeCl3 may be intercalated between one or more of the graphene layers to reduce the element resistance. For example, such a technique is described in more detail in the publication entitled "<NPL>.

In plan view (not represented in <FIG>), the graphene film <NUM> may have any shape, and for example has a surface area of anywhere between <NUM>µm2 and <NUM> cm2, depending on application.

The graphene film <NUM> is covered by a support <NUM> in the form of a layer of polymer material. The polymer material is selected from the family of n-xylylenes, and in one example comprises parylene. Parylene has the advantage of being capable of being stretch by up to <NUM>% before breaking, and is capable of remaining flexible over a relatively wide temperature range. In one example, the polymer material comprises parylene C or parylene N. Both parylene C and parylene N have the advantage of being relative elastic, while parylene N has a slightly lower Young's modulus, and thus a higher elasticity, than parylene C.

As will be described in more detail below, the polymer support <NUM> has been formed by a gas phase deposition technique. The polymer support <NUM> has a thickness of between <NUM> and a few tens or hundreds of µm, up to <NUM>, depending on the application.

While in the example of <FIG> the polymer support is in the form of a layer having a substantially uniform thickness, as will become apparent from the embodiments described below, the polymer support could take other forms, depending on the particular application.

The combination of a graphene film <NUM> and a polymer support <NUM> provides a multi-layer that can have relatively high electrical conductance while remaining flexible and strong. Of course, while in the multi-layer of <FIG> there are just two layers - the graphene layer and the parylene layer that form a bi-layer, in alternative embodiments there could be one or more further layers. For example, the graphene layer could be sandwiched by parylene layers on each side, and/or one or more layers of further materials could be formed in contact with the graphene or parylene layer.

Furthermore, the use of a polymer such as parylene leads to a device that is biocompatible, making the device suitable for a variety of applications in which it can for example contact human or animal tissue.

<FIG> illustrates apparatus <NUM> for forming a graphene device such as the device of <FIG> according to an example embodiment.

The step of forming the graphene film <NUM> for example involves forming mono-layers of graphene using the apparatus <NUM>. A similar apparatus is described in the publication entitled "<NPL>.

The apparatus <NUM> comprises a reaction chamber <NUM> in which the graphene film is formed. For example, the reaction chamber <NUM> is a tube furnace or other type of chamber that can be heated.

A substrate <NUM>, for example formed of a copper foil having a thickness of between <NUM> and <NUM>, is placed within the chamber <NUM>. The substrate <NUM> provides a surface suitable for graphene formation. In particular, the material of the substrate <NUM> is for example selected as one that provides a catalyst for graphene formation, and for example has relatively low carbon solubility. For example, other possible materials for forming the substrate <NUM> include other metals such as nickel, cobalt, or ruthenium or copper alloys such as alloys of copper and nickel, copper and cobalt, copper and ruthenium, or dielectric materials, such as zirconium dioxide, hafnium oxide, boron nitride and aluminum oxide. In some embodiments, rather than being a foil, the substrate <NUM> could have a 3D form. The dimensions of such a substrate <NUM> could be anywhere from <NUM> to several cm or more. Furthermore, the substrate <NUM> could be formed on a planar or 3D surface of a further substrate, for example of copper or another material such as sapphire.

An inlet <NUM> of the reaction chamber <NUM> allows gases to be introduced into the chamber, and an outlet <NUM> allows gases to be extracted from the chamber. The inlet <NUM> is for example supplied with gas by three gas reservoirs 210A, 210B and 210C, which in the example of <FIG> respectively store hydrogen (H2), argon (Ar), and methane (CH4). In alternative embodiments discussed in more detail below, different gases could be used. In particular, rather than hydrogen, a different etching gas, in other words one that is reactive with carbon, could be used, such as oxygen. Rather than argon, another inert gas could be used, such as helium. This gas is for example used to control the overall pressure in the reaction chamber <NUM>, and could be omitted entirely in some embodiments. Rather than methane, a different organic compound gas could be used, such as butane, ethylene or acetylene.

The inlet <NUM> is coupled to: reservoir 210A via a tube 212A comprising a valve 214A; reservoir 210B via a tube 212B comprising a valve 214B; and reservoir 210C via a tube 212C comprising a valve 214C. The valves 214A to 214C control the flow rates of the respective gases into the chamber.

The valves 214A to 214C are for example electronically controlled by a computing device <NUM>. The computing device <NUM> for example comprises a processing device <NUM>, under the control of an instruction memory <NUM> storing program code for controlling at least part of the graphene formation process.

The outlet <NUM> is for example coupled via a tube <NUM> to an evacuation pump <NUM> for evacuating gases from the reaction chamber <NUM>. The rate of evacuation by the pump <NUM> is for example also controlled by the computing device <NUM>. As represented by an arrow <NUM>, the computing device may also control one or more heating elements of the reaction chamber <NUM> to heat the interior of the chamber during the graphene formation process.

A method of forming a graphene film using the apparatus described above is for example discussed in more detail in the US patent application published as <CIT>.

Furthermore, a deposition chamber <NUM> is for example provided for depositing the polymer layer over the graphene film. In the embodiment of <FIG>, a trapdoor <NUM> in one wall of the chamber <NUM> and a passageway <NUM> between the chambers <NUM>, <NUM> permit the substrate <NUM> with graphene film to be transferred between the chambers <NUM> and <NUM> without being exposed to the atmosphere. In alternative embodiments, the deposition chambers <NUM> and <NUM> could be separate from each other, and the substrate <NUM> with graphene film could be transferred without using a passageway.

The deposition chamber <NUM> for example comprises an inlet <NUM> coupled via a further valve 214D to a supply chamber <NUM> for providing a precursor for depositing the polymer material to cover the graphene film. The valve is for example controlled by the computing device <NUM>. As mentioned above, the polymer material is deposited using gas phase deposition. The term "gas phase deposition" is considered here to include physical vapor deposition (PVD), chemical vapor deposition (CVD and atomic layer deposition (ALD). The precursor is for example heated in the supply chamber <NUM> to between <NUM> and <NUM> before being introduced as a vapor phase into the chamber <NUM> via the valve 214D.

<FIG> are cross-section views of a graphene device during its fabrication, for example using the apparatus of <FIG>.

As shown in the <FIG>, initially it is assumed that a graphene film <NUM> has been formed by CVD over a substrate <NUM>, which is for example a copper foil.

<FIG> illustrates an operation in which the polymer support is deposited covering the graphene film <NUM>. In the example of <FIG>, the graphene is deposited over a relatively flat substrate <NUM>, and the polymer material is deposited as a conformal layer <NUM> of substantially uniform thickness that encapsulates the device, including the substrate <NUM>. For example, the device is suspended such that the polymer is deposited on all faces of the device. Alternatively, the device could be turned over during the deposition process. In yet further alternative embodiments, the polymer material could be deposited only over the graphene film <NUM>. Furthermore, rather than being deposited in the form of a layer, the polymer material could be deposited in other forms, as will be described in more detail below.

<FIG> illustrates a subsequent operation in which the substrate <NUM> is removed, for example by an etching step or by delaminating the polymer layer with the graphene film <NUM> from the substrate <NUM>. For example, the etching step involves removing the polymer coating covering the substrate <NUM>, for example using a plasma etch, or by scraping with a sharp blade, in order to expose the surface of the substrate. The substrate is then removed, for example using a suitable etch, such as an acid etch or using an electrolysis technique. For example, an electrochemical delamination process may be performed as described in more detail in the publication entitled "<NPL>et al.

This leaves the graphene film <NUM> with the polymer support <NUM>. The present inventors have found that this polymer support <NUM> not only repairs to some extent any defects in the graphene film <NUM>, but also limits further degradation of the graphene film <NUM> during the separation of the graphene film <NUM> from the substrate <NUM>.

An advantage of the process described herein is that no transfer operation is required, reducing the risk that the properties of the graphene film will be degraded.

Indeed, graphene is generally formed using a chemical vapor deposition (CVD) process, wherein graphene is formed over a base substrate such as a copper foil. However, a difficulty is that it is relatively difficult to remove the graphene layer from the base substrate without damaging or polluting the graphene layer and/or degrading its conductivity.

By depositing a polymer material by gas phase deposition in contact with the graphene film, the polymer can remain attached to the graphene while the substrate is removed, for example by etching or by a delamination process, without a transfer step.

The process for forming a graphene device as described in relation to <FIG> may be adapted to form a number of particular graphene devices as will now be described with reference to <FIG>.

<FIG> are cross-section views showing steps in a method of forming a graphene device comprising a three-dimensional graphene film according to an example embodiment. For example, such a device is suitable for being placed on or over a 3D form, such as a human or animal member, or a device or part of a device, and for example provides the function of a sensor, of a protection barrier, or the like.

<FIG> illustrates an example of a cross-section of a mold <NUM> over which the graphene device is to be formed. The 3D form of this mold <NUM> shown in <FIG> is merely one example used for illustration, and many different forms would be possible, depending on the particular application. The mold is formed of a material supporting graphene growth, such as copper.

<FIG> illustrates operations in which a graphene film <NUM> is formed over the mold <NUM>, and a coating of polymer, such as of parylene, is then deposited over the graphene film <NUM>.

<FIG> illustrates a subsequent operation in which the mold is removed, for example for example by an etching step or by delaminating the polymer layer with the graphene film <NUM> from the substrate <NUM>, for example using a delaminating operation as described above.

<FIG> illustrates a sensing device <NUM>, which in this example is designed to be worn by a user over their index finger or other body part. Of course, the technique that will be represented in relation to <FIG> could be applied a variety of different types of sensors having one or more sleeves or tubes adapted to fit around a body part of a human or animal. For example, the sensor could be in the form of a glove with a sensor in each finger of the glove in order to detect finger movements.

The sensor device <NUM> of <FIG> comprises a layer of a polymer such as parylene in the form of a sleeve or tube <NUM> that has dimensions closely fitting an index finger of a user. In the example of <FIG>, the sleeve <NUM> is closed at one end to form a finger. A film of graphene is formed on a portion of the inside surface of the sleeve <NUM>, and provides an electrode <NUM> and conductive track <NUM>. The electrode <NUM> is positioned to contact a portion of the underside of a finger near the tip of the finger. The electrode <NUM> is coupled via the conductive track <NUM> to an end <NUM> of the sleeve <NUM> opposite to the fingertip. While not shown in <FIG>, the end of the conductive track may be coupled via a wire to monitoring equipment, or a monitoring device could be implemented by an integrated circuit mounted on a side of the sleeve <NUM>.

<FIG> are cross-section views of the sensor device <NUM> of <FIG> during process steps for forming the sensor device of <FIG>. The cross-sections of <FIG> for example correspond to a line A-A shown in <FIG>, that passes through a portion of the sleeve <NUM> close to the fingertip and passing through the electrode <NUM>.

As represented in <FIG>, a finger-shaped mold <NUM> of the same or approximately the same dimensions as the index finger to be used in the sensing device <NUM> is formed, for example of a material that does not support graphene growth, such as aluminum oxide. A thin plating <NUM> of a material such as copper, which supports graphene growth, is formed in the zone in which the electrode <NUM> and conductive track <NUM> are to be formed.

For example, in order to form the plated material <NUM> of copper or another material, one of two processes could be used.

A first process is for example described in more detail in the publication by <NPL>. According to such a lithography process, an electron or photon sensitive resin is evaporated depending on the type of lithography to be used and on the desired resolution. Such a resin can be applied to non-planar surfaces in a desired pattern, followed by a lithography operation.

A second process is for example described in more detail in the publication by <NPL>). According to this technique, a resin film is prepared in advance by spin-coating and annealing. After this annealing, the resin film becomes solid and flexible, and can be transferred to the non-planar surface and follows it its 3D form. A lithography step can then be performed.

As represented in <FIG>, the mold is then for example placed in a CVD chamber such as the chamber <NUM> of the apparatus of <FIG>, and a graphene film <NUM> is selectively formed over the plating <NUM>. The polymer layer in the form of the sleeve <NUM> is then formed by coating a layer of polymer over the mold, including over the graphene film <NUM>. The polymer coating for example has a thickness of between <NUM> and <NUM>. Where this polymer coating contacts the graphene film <NUM>, it provides the polymer support for the graphene film <NUM>.

As represented in <FIG>, polymer sleeve <NUM>, and the graphene film <NUM>, are for example removed from the mold, for example by a delamination process or electrochemical delamination process as described above.

While in the example of <FIG> the sensing device <NUM> comprises a single graphene conductive track <NUM> leading to a graphene plate forming the electrode <NUM>, many other arrangements would be possible, as will now be described with reference to <FIG>.

<FIG> illustrates the form of a graphene film <NUM> of the sensing device <NUM> of <FIG> according to one example in which two conductive tracks <NUM>, <NUM> are provided leading to the electrode, and the electrode is implemented in the form of a meandering track electrically connecting the track <NUM> to the track <NUM> and formed with a detection zone <NUM>. The tracks <NUM>, <NUM> and the meandering track are for example formed using the lithography or spin-coating process described above with relation to <FIG>.

The conductive tracks <NUM>, <NUM> are for example coupled to a detection circuit <NUM> for detecting a change in resistance of the conductive track formed in the detection zone. For example, the circuit <NUM> is adapted to apply a substantially constant current through the conductive tracks <NUM>, <NUM> and to monitor the voltage drop between the conductive tracks <NUM>, <NUM>. Pressure applied to the graphene film in the zone <NUM> for example causes a change in the resistance of the graphene film by deforming the graphene film and/or causing a short circuit between sections of the meandering conductive track. Such a change in the resistance brings about a corresponding change in the voltage across the conductive tracks, which is detection by the detection circuit <NUM>.

In one example, the sensing device of <FIG> is used in a key stroke detection system, as will now be described in more detail with reference to <FIG>.

<FIG> illustrates a virtual keyboard system in which a projector <NUM> is provided, in this example mounted on top of a display <NUM>. The projector <NUM> projects an image <NUM> of a user interface onto a surface. In the example of <FIG>, the user interface is a keyboard, but in alternative examples, other types of user interface can be projected. For example, the screen image could be projected in order to provide the functionality of a touch-screen. In such a case, the display <NUM> could be omitted.

The system also for example comprises a 3D ranging camera for detecting typing events made by a user on the projected image of the keyboard. Such a virtual keyboard system is for example discussed in the publication by <NPL>.

A difficulty in such a virtual keyboard system is to confirm a typing event that has been detected visually. For example, a user may move a finger towards a key position with the intention of making a typing stroke, but then pull-back just short of touching the key position. Such a non-completed key stroke may be interpreted as an actual key stroke if based on visual data alone.

To deal with this problem, the user for example has one or more sensing devices similar to the ones of <FIG> and <FIG> attached to one or more fingers. For example, the user wears gloves <NUM>, <NUM> on their right and left hands respectively, comprising such a sensing device in one, several or all of its fingers.

While the meandering graphene track of <FIG> provides one possible means of detecting an exerted pressure in the detection zone <NUM>, other techniques may be employed, as will now be described with reference to <FIG>.

<FIG> is a plan view of a sensing apparatus comprising a pair of graphene films, respectively comprising conductive track <NUM> and <NUM>. The conductive track <NUM> is connected at one end to a graphene plate <NUM>, while the conductive track <NUM> is connected at one end to a graphene plate <NUM>. The graphene plates <NUM>, <NUM> are arranged such that they overlap, and they are separated by a deformable insulating layer (not illustrated in <FIG>) such that they have an associated capacitance. An external compressive force applied to the plates <NUM>, <NUM>, for example caused by a finger hitting a surface, will thus change the distance between the plates and cause a change in their capacitance, which can be detected by a detection circuit <NUM> coupled to the conductive tracks <NUM>, <NUM>.

<FIG> is a cross-section view of a sensing device <NUM> similar to the device <NUM> of <FIG>, but adapted to comprise the sensing apparatus of <FIG>.

The device <NUM> for example comprises an outer polymer sleeve <NUM>, having formed therein the plate <NUM> and the conductive track <NUM> (not illustrated in <FIG>) running along the length of the sleeve. Such a structure is for example formed by the process described with reference to <FIG>. The device <NUM> also for example comprises an inner polymer sleeve <NUM>, having formed, on an outer surface thereof, the graphene plate <NUM>, positioned adjacent to the graphene plate <NUM>, and the conductive track <NUM> (not illustrated in <FIG>). This structure may also be formed by the method of <FIG>, and by then turning the finger inside-out such that the graphene plate <NUM> is on the outside of the inner polymer sleeve <NUM>. The polymer sleeve <NUM> is then positioned as an inner lining of the polymer sleeve <NUM> to achieve the structure of <FIG>. The graphene plates <NUM>, <NUM> are separated by an insulating layer <NUM> for example formed of polymer, and which may comprise a polymer coating formed over the graphene plate <NUM> and/or a polymer coating formed over the graphene plate <NUM>.

In use, the sensing device <NUM> is placed over a finger or other body part. A charge is then for example stored on one of the plates <NUM>, <NUM> by applying a voltage between the conductive tracks <NUM>, <NUM>, for example by the detection circuit <NUM>. The graphene plates <NUM>, <NUM> then form a detection zone such that if pressure is applied in this zone, the capacitance of the plates <NUM>, <NUM> will change, causing a change in the voltage on the conductive tracks <NUM>, <NUM>. This voltage change can be detected by the detection circuit <NUM>.

An advantage of the graphene device described herein is that the polymer layer supports the graphene film <NUM>, helping to maintain relative high conductive properties of the graphene film <NUM> as it is removed from the mold.

Furthermore, by depositing the polymer layer using gas phase deposition, the electrical conducting properties and mechanical properties of the graphene film can be particularly well conserved as the mold is removed. Indeed, gas phase deposition allows a thin polymer coating of relatively uniform thickness to be applied that has high conformity with the roughness of the surface of the graphene film, by closely following the contours of the graphene film. In view of its high conformity and uniformity, such a polymer layer exerts a lower stress on the graphene layer than would be possible with other deposition techniques such as spin coating.

Furthermore, gas phase deposition allows a supporting polymer layer to be realized that strictly conforms to a <NUM>-dimensional shape of the graphene film, both at the nanoscale and at the microscale, respectively helping to preserve the integrity of the film by matching the wrinkles and thereby providing good electrical conductivity and helping to maintain the global 3D shape of the graphene film after the mold removal, allowing depositions on complex shapes such as gloves, etc..

Claim 1:
A method of forming a graphene device, the method comprising:
- forming a graphene film (<NUM>) over a substrate (<NUM>) , wherein the thickness of the graphene film is from one atom to <NUM> atom layers;
- depositing, by gas phase deposition, a polymer material from the n-xylylene family covering a surface of the graphene film (<NUM>) ; wherein the polymer layer is deposited with a thickness of between <NUM> and <NUM>, and
- removing the substrate (<NUM>) from the graphene film (<NUM>) , wherein the polymer material from the n-xylylene family forms the support (<NUM>) for the graphene film (<NUM>) .