Devices that interact with electromagnetic radiation

Abstract

The present disclosure relates to a chip that interacts with electromagnetic radiation and a method for fabricating a device that interacts with electromagnetic radiation. The method for fabricating the device includes disposing an unpatterned graphene layer on a substrate that includes an unpatterned metal layer to form an unpatterned graphene-metal bilayer attached to the surface of the substrate. The method then includes patterning the bilayer with a design that includes one or more overlapping trenches through the graphene layer and the metal layer. Each of the one or more trenches extends through the graphene layer and the metal layer to provide for interaction with electromagnetic radiation.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from Australian Provisional Patent Application No. 2021 / 901438, filed on May 14, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates to a chip that interacts with electromagnetic radiation and a method for manufacturing the chip. [Background technology]

[0003] Although a wide range of antennas and other devices that absorb electromagnetic radiation are available for use in a variety of different application scenarios, design challenges remain. Specifically, as the frequency of the electromagnetic radiation that the device is intended to absorb increases, traditional designs become ineffective. Primarily, the metallic conductors used in traditional antennas become lossy at higher frequencies, thus leading to reduced effectiveness, resulting in an insufficient amount of energy from the electromagnetic radiation being absorbed by the device.

[0004] In the terahertz (THz) range, there are theoretical designs of new materials and devices that have been shown in simulations to absorb electromagnetic radiation, but their fabrication remains difficult. As a result, few experimental results and example physical antennas are available. Thus, there is a need for absorbers with tunability or reconfigurability, effective and physically realizable designs.

[0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in this specification should not be deemed an admission that any or all of such matters form part of the prior art base or are common general knowledge in the field relevant to the present disclosure by virtue of having existed prior to the respective priority date of the appended claims.

[0006] Throughout this specification the word "comprise" or variations such as "comprise" or "comprising" will be understood to mean the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Summary of the Invention [Means for solving the problem]

[0007] The present disclosure provides a device that interacts with electromagnetic radiation, for example in the sub-terahertz wavelength range. The disclosed device comprises a dielectric layer covered by a bilayer of metallic conductive material, such as gold, for frequency selective interactions, such as absorption, and graphene for tunability. The bilayers are patterned together to provide a superimposed pattern on the conductive metal and graphene. As a result, a tip can be fabricated by depositing the conductive metal first, the graphene second, and then patterning both by a two-step etching process, providing interactions at tunable amplitude and frequency by adjusting the bias voltage applied to the graphene. Furthermore, in some areas, the graphene is in direct contact with the dielectric layer, resulting in improved adhesion of the graphene to the tip.

[0008] A method for manufacturing a device includes: disposing an unpatterned graphene layer on a substrate including an unpatterned metal layer to form an unpatterned graphene-metal bilayer attached to a surface of the substrate; patterning a bilayer through the graphene layer and the metal layer in a design including one or more overlapping trenches; The one or more trenches each extend through the graphene layer and the metal layer to provide for interaction with electromagnetic radiation.

[0009] In some embodiments, the patterning is performed using a single mask that defines a design, thereby creating trenches through the graphene layer and the metal layer in a single patterning step.

[0010] In some embodiments, the method further includes using a single mask to perform both the etching of the graphene layer and the etching of the metal layer.

[0011] In some embodiments, the method comprises: Etching the graphene layer with a first etchant; After etching the graphene layer, the method further includes etching the metal layer with a second etchant.

[0012] In some embodiments, etching the graphene layer comprises use of an oxygen plasma and etching the metal layer comprises use of an argon plasma.

[0013] In some embodiments, the method further includes disposing an unpatterned metal layer on the substrate.

[0014] In some embodiments, the method further includes creating a gap in the metal layer to define the first electrode and the second electrode.

[0015] In some embodiments, creating the gap includes using a mask on the metal layer and etching the metal layer or using a directed beam.

[0016] In some embodiments, the gaps are created prior to disposing the unpatterned graphene layer on the substrate.

[0017] In some embodiments, the method further comprises cleaning the device with an oxygen plasma during or after patterning.

[0018] In some embodiments, patterning the bilayer includes creating one or more trenches in the graphene and metal layers of the bilayer using a directed beam.

[0019] The device is a support layer having a first surface; a patterned graphene-metal bilayer comprising a metal layer deposited on the first surface and a graphene layer deposited on the metal layer, the bilayer including one or more overlapping trenches extending through the graphene layer and the metal layer to provide for interaction with electromagnetic radiation; overlapping trenches are aligned across the graphene layer and the metal layer by patterning the bilayer; the metal layer includes a gap to define a first electrode including one or more overlapping trenches and a second electrode; A first electrode is connected to a second electrode by a graphene layer to provide tunability by varying a voltage applied between the first and second electrodes and across the graphene layer parallel to the first surface.

[0020] In some embodiments, the second electrode is on top of the graphene.

[0021] In some embodiments, the one or more trenches define an array, and the array extends across the bilayer.

[0022] In some embodiments, the array is a periodic design to provide for interaction with electromagnetic radiation by the device.

[0023] In some embodiments, the patterned bilayer forms a metamaterial structure.

[0024] In some embodiments, the support layer is a dielectric layer.

[0025] In some embodiments, the device includes a resonant structure including a dielectric layer that is tunable by a voltage applied across the graphene layer to thereby tune the interaction with electromagnetic radiation.

[0026] In some embodiments, the dielectric layer has a second surface opposite the first surface; The device further includes a reflective conductive layer disposed on the second surface for reflecting electromagnetic radiation propagated through the dielectric layer back to the dielectric layer to create a resonance within the dielectric layer.

[0027] In some embodiments, the support layer is constructed from a fiberglass and polytetrafluoroethylene (PTFE) composite material.

[0028] In some embodiments, the electromagnetic radiation has a frequency between 1 GHz and 3 THz.

[0029] In some embodiments, the electromagnetic radiation has a frequency between 100 GHz and 3 THz.

[0030] In some embodiments, the electromagnetic radiation has a frequency greater than 100 GHz.

[0031] In some embodiments, the metal layer is composed of gold.

[0032] In some embodiments, the metal layer is thicker than the skin depth of the electromagnetic radiation in the metal layer.

[0033] In some embodiments, the graphene layer extends beyond the metal layer and is directly attached to the support layer.

[0034] In some embodiments, the graphene layer comprises: a gap between the first electrode and the second electrode; and In one or more of the regions around the periphery of the metal layer, it is directly attached to the support layer.

[0035] The device is a support layer having a first surface; a metal layer disposed on the first surface; a graphene layer disposed on the metal layer; the metal layer and the graphene layer form a bilayer; The graphene layer extends beyond the metal layer and is directly attached to the support layer.

[0036] In some embodiments, the support layer is a dielectric layer.

[0037] In some embodiments, the graphene layer is directly attached to the support layer by an adhesive force between the graphene layer and the support layer.

[0038] In some embodiments, the bilayer includes one or more trenches to provide for interaction with electromagnetic radiation in the bilayer; One or more trenches extend through the graphene layer and the metal layer.

[0039] A method for manufacturing a device includes: disposing a metal layer on a support layer, where an area of ​​the support layer is exposed; disposing a graphene layer on the metal layer to form a bilayer including the metal layer and the graphene layer, with the graphene layer directly contacting the exposed area of ​​the support layer.

[0040] Examples will now be described with reference to the following drawings. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 shows a tip for absorbing electromagnetic radiation. [Diagram 2] FIG. 2 illustrates a further exemplary chip. [Diagram 3] FIG. 1 illustrates yet a further exemplary chip. [Figure 4] FIG. 1 illustrates a method for manufacturing a chip. [Diagram 5]FIG. 1 illustrates another method for manufacturing a chip. [Figure 6] Experimental setup for terahertz time-domain spectroscopy in reflection geometry: Terahertz waves are reflected from a graphene / gold bilayer metasurface functioning as a single-port device. [Figure 7] FIG. 1 provides a schematic of a graphene / gold bilayer metasurface integrated into a 0.2 THz frequency selective absorber. The top panel shows the unit cell and array structure, the bottom right panel depicts the graphene / gold structure on a 0.254 mm Rogers 5880LZ substrate, and the bottom left panel displays an image of the fabricated device. [Figure 8] FIG. 8 shows a cross-section of a 0.2 THz frequency selective absorber as shown from the intersecting black planes of FIG. [Figure 9] Figure 1 shows an SEM image of pattern 108. The length of the arms of each cross is about 100 μm. The picture was taken at EHT=5 kV, Mag=118X, WD=5.1 mm, aperture size=30.00 μm. [Figure 10] Figure 7 shows the S11 parameters obtained from the experimental setup of Figure 6. Clear frequency tuning of 5 GHz of the 0.2 THz resonance and amplitude tuning of 16 dB (approximately 97.5%) are observed for applied DC voltages from 1 to 6 V. [Figure 11] FIG. 1 shows the broadband response of the device to applied voltages of 0 V and 6 V. Clear resonances and broadband modulations are observed. [Figure 12] Figure 1 shows the S11 parameters of the designed 0.2 THz resonance, demonstrating a clear frequency tuning of 5 GHz and an amplitude tuning of 16 dB (approximately 97.5%). The top and bottom panels show the reversal of the voltage connections. [Figure 13] Figure 14 Voltage characteristics of the 0.2 THz mode: The peak position, S11 parameter, FWHM and peak area all show nonlinear behavior with systematic changes in the region above an applied voltage of 3 V. [Figure 14]Broadband response of the absorber. The left panel presents a comparison of the gold / graphene bilayer metasurface (red) with its gold-only counterpart (black). All plasmonic modes between 0.2 and 0.6 THz are reproduced with increased losses and small frequency shifts. Modes above 0.6 THz are not reproduced in the bilayer. The right panel shows the full frequency response of the bilayer with applied voltage. Frequency and amplitude tuning is observed for each resonance superimposed on the broadband modulation. [Figure 15] FIG. 13 shows the simulated S11 parameters of the gold-only metasurface response at 0.2 THz. [Figure 16] The broadband modulation depth of the bilayer is shown: A discontinuity is seen at the resonant frequency due to the frequency shift of these modes with applied electric field. [Figure 17] (a) Experimental comparison of the graphene / gold bilayer metasurface (bottom line) and its gold-only counterpart (top line). The 0.2 THz absorption is reproduced with increased amplitude and a slight frequency red-shift. (b) Simulated S11 parameters of the graphene / gold metasurface (bottom line) and its gold-only counterpart (top line). An increase in the resonance amplitude and a red-shift of the mode are produced in both the experimental and simulated results, and strong agreement between the two is observed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Electronic systems in the THz frequency band are usually accompanied by relatively high spurious tones and parasitic intermodulation due to frequency multiplication, heterodyne mixing and amplification networks. State-of-the-art frequency-selective absorbers are desired to eliminate these undesired interferences at specific frequencies while imparting little attenuation to the available signal. The respective absorption amplitude or frequency needs to be electrically tunable to overcome the unpredictability of the parasitic interferences and thus greatly increase the flexibility of the signal processing. However, electrically tunable frequency-selective THz absorbers with reasonably high quality factor resonances remain elusive. A possible archetype in achieving such desired high quality resonances is in the realm of THz metamaterials as disclosed herein.

[0043] Metamaterials consist of periodic arrays of subwavelength unit cells and exhibit properties not available from natural materials. Such structures mimic the periodicity of crystal lattices, allowing for control of response to and manipulation of the amplitude, polarization, and phase of electromagnetic radiation.

[0044] Graphene is a two-dimensional (2D) material with unique features that make it a strong candidate for next-generation THz electronic devices: (i) high charge carrier mobility that enables ultrafast response to electric and magnetic fields required at THz frequencies; and (ii) a Dirac band structure with linear dispersion that results in charges behaving as massless Dirac fermions, such that the Fermi level and, therefore, the electrical conductivity can be tuned with the application of an external field.

[0045] Terahertz radiation The present disclosure provides a patterned device chip for absorbing THz electromagnetic radiation. In a general sense, a chip is a small piece of material on which a specific function is implemented. In many embodiments, the chip has a dielectric substrate that is used as a carrier for functional elements that are integrated on the same substrate. Many chips are fabricated using lithography as digital processing chips on silicon substrates, but other applications and substrates are possible. Here, the disclosed chips are also fabricated on substrates such as polytetrafluoroethylene (PTFE), and functional elements are applied on the substrate to provide absorption of electromagnetic radiation by the chip. In one embodiment, the substrate is a Rogers 5880 high frequency laminate circuit board. It is a glass microfiber reinforced PTFE composite, consisting of about 70% PTFE. In other embodiments, the substrate may be PTFE, polyimide and other polymers / plastics, or flexible substrates such as sapphire, MgO, silicon, etc. The disclosed chips are particularly useful in the sub-millimeter (sub-mm) wavelength band, but there is no strict physical limitation for application to longer wavelengths. In this sense, the disclosed chip may be designed to operate at millimeter or longer waves, but other technologies are expected to outperform the proposed chip in cost, and therefore the main application area is expected to be in the sub-millimeter band.

[0046] The International Telecommunications Union (ITU) defines Extremely High Frequency (EHF) as 30 to 300 Gigahertz (GHz) with wavelengths of 10 to 1 mm. Submillimeter waves (Tremendously High Frequency, THF) are then defined as frequencies of 0.3 to 3 Terahertz (THz), occupying a band roughly between microwaves and infrared light. Within such an ITU definition, some embodiments of the present disclosure are expected to apply the upper end of the EHF frequency band and the THF frequency band. This band is also referred to as the Terahertz band and may be defined as 0.1 to 10 THz. In the Terahertz band, electromagnetic radiation absorption technology is in its infancy. Some embodiments disclosed herein are capable of absorbing electromagnetic radiation within the Terahertz band. However, it should be noted that the principles disclosed herein may be applied outside the Terahertz band.

[0047] One exemplary application is in the sixth generation (6G) of mobile communications. The current fifth generation (5G) occupies the 30-300 GHz band, but future 5G and 6G bands are expected to be in the terahertz band. Similar to mm-band communications, the terahertz band can be used as mobile backhaul to transmit wideband signals between base stations. Another location for fiber or copper exchange is point-to-point links in rural environments, and macrocell communications.

[0048] More importantly, the terahertz band can be used in close-proximity communications, also known as whisper radio applications. This includes circuit boards and transmissions, nanosensors, and wiring harnesses in wireless personal area networks (PANs). Then there are applications such as high-resolution spectroscopy and imaging and communications research, which use short-range communications in the form of large bandwidth channels with zero error rates in key areas such as coding, redundancy, and frequency diversity.

[0049] Tips FIG. 1 shows a chip 100 for interacting with (including but not limited to absorbing) electromagnetic radiation, such as radiation in the THz band. A chip in this context is a small electronic device fabricated on a thin substrate. In one application, the chip 100 may be designed to absorb radiation as its interaction, and is therefore referred to as an absorber or simply an absorber of electromagnetic radiation. In other applications, the chip 100 may function, for example, as a sensor. In still further embodiments, the chip 100 is designed for reflection, refraction, diffraction, and deflection. All wave-matter interactions can be summarized in these four interactions above. Thus, the chip 100 may also be designed for absorption, interference, modulation, steering, transmission, polarization, phase shifting, amplification, attenuation, focusing, and potentially further interactions. As disclosed herein, the geometric design of the chip determines which of the above functions are implemented. Although chip 100 is shown as is, it should be understood that chip 100 may be interfaced with electrical connections, packaged in a suitable casing, or integrated with other components on the same substrate or on a separate substrate.

[0050] support layer The chip 100 includes a support layer 101, also referred to herein as dielectric layer 101, having a bottom surface 102 and a top surface 103 opposite the bottom surface 102. In some examples described herein, the top surface 103 is referred to as the "first surface" and the bottom surface 102 is referred to as the "second surface." The dielectric layer 101 can be made of a variety of materials that are essentially transparent, i.e., have low absorption, to the electromagnetic radiation absorbed by the chip 100. Typically, dielectric materials are insulating or conduct little electrical current. In some examples, the dielectric constant of the dielectric material is:

[0051]

number

[0052] or less, and the dissipation factor may be 0.002-0.003 at 10 GHz. A wide range of materials may be used, including ceramics, air, and polymers. The dielectric layer 101 may be, for example, SiO 2 The dielectric layer 101 may be made from many dielectric materials such as most metal oxides such as MgO, fiberglass or sapphire. In some embodiments, the dielectric layer 101 may include multiple layers of dielectric material. The dielectric layer may also be a vacuum layer, but mechanical placement may be difficult. In other embodiments, the dielectric layer 101 may be made of polytetrafluoroethylene (PTFE) and may be a composite or laminate material. In some embodiments disclosed herein, the dielectric layer 101 is a RT / duroid 5880LZ laminate substrate manufactured by Rogers Corporation. During the manufacture of the sensor 100, as described in more detail below, the dielectric layer may be used as a starting point. Thus, the dielectric layer is also referred to herein as the "substrate."

[0053] reflective layer The chip 100 further includes a ground electrode 104, which is essentially a reflective conductive layer disposed on the bottom surface 102 to reflect electromagnetic radiation propagated through the dielectric layer 101 back to the dielectric layer 101 to form a resonance within the dielectric layer 101. The ground electrode 104 may be made of a variety of different reflective conductive materials, including metals such as aluminum, copper, and others. In another embodiment, the reflective layer may be graphene, or a graphene / metal bilayer. The ground electrode 104 may also be made of a doped semiconductor. In one embodiment, the ground electrode 104 is made of gold, which has the advantages of good electrical conductivity and ease of manufacture. In use, the ground electrode 104 may be connected to ground or another reference potential.

[0054] double layer There is also a metal layer 105 and a graphene layer 106, which together form a bilayer 107. The metal layer 105 is disposed on the top surface 103 and is configured by patterning an array of slot antennas to interact with electromagnetic radiation resonating in the dielectric layer 101 as reflected by the bottom reflective layer 104, which can be tuned by applying a voltage to the graphene layer 306.

[0055] Also, the metal layer 105 can be made of a range of metals and metal alloys, including Ti / Au, Cr (chromium), W (tungsten), aluminum and copper. Note that in some embodiments disclosed herein, the metal layer 103 is made of gold, and the bottom reflective layer 104 and the top metal layer 105 can be made of the same or different materials. The thickness of the metal layer is greater than the skin depth of the electromagnetic radiation in the metal layer, e.g., 167 nm at 0.2 THz for gold. The skin depth is the depth from the surface where the amplitude of the electromagnetic wave is attenuated to less than 1 / e of the amplitude at the surface of the conductor.

[0056] Disposed on the top metal layer 105 is a graphene layer 106. The graphene layer 106 provides tunability to the resonance and thereby the absorption of the graphene / metal bilayer metastructure 107 when applied with a DC bias voltage. As a result of the graphene layer 106 being disposed on the metal layer 105, the metal layer 105 and the graphene layer 106 form a bilayer 107. The term "bilayer" is used herein to indicate that the graphene 106 and the metal 105 essentially form a single electrode layer having two portions, namely the metal layer 105 and the graphene layer 106. The metal layer 105 and the graphene layer 106 together form the same metastructure or metamaterial as the bilayer 107, which has properties that are particularly advantageous for the absorption of electromagnetic THz radiation and have amplitude and frequency tunability. A metastructure or metamaterial (which may simply be referred to as a metamaterial structure) is any material that has been engineered to have properties not typically found in naturally occurring materials. Metamaterial structures such as the graphene / metal bilayer 107 may also include metasurfaces that can modulate the behavior of electromagnetic waves through specific boundary conditions.

[0057] Since the metal layer 105 and the graphene layer 106 form the bilayer 107, the bilayer is continuous, meaning that it forms a single electrode. This is in contrast to other designs where there are multiple islands of metal and graphene layers that are discontinuous. Such islands may be connected by separate wires or other means, but in such cases the bilayer is not continuous. Here, both the metal layer 105 and the graphene layer 106 are continuous (i.e., uninterrupted) as a continuous bilayer. In other words, the pattern 108 includes voids where a portion of the bilayer has been removed. As a result, such voids are surrounded by the continuous bilayer, meaning that the bilayer is not divided by the pattern. In a geometrical sense, all points in the active area of ​​the bilayer around the pattern are reachable from all other points in that area only through the bilayer. That is, no wires or other structures are required between any two points in the active area of ​​the bilayer around the pattern. In view of the above disclosure, it is also considered reasonable to refer to the bilayer as a continuous interacting layer.

[0058] In other words, the bilayer is continuous and spans a substantial portion of the first surface prior to patterning, covering a large portion of the pattern. Furthermore, after patterning the bilayer, the bilayer is still continuous and spans a substantial portion of the first surface of the support layer. The bilayer also constitutes a bonded or tightly bonded graphene-metal metastructure that spans the surface of the substrate forming a continuous, tunable conductive layer. When viewed from above, it can be seen that the bilayer is continuous from left to right as well as from top to bottom. The bilayer is continuous from left to right in the sense that there is an unbroken / continuous line or path that starts at the left edge of the bilayer and ends at the right edge of the bilayer. The bilayer is continuous from top to bottom in the same sense.

[0059] When a voltage is applied to the graphene layer 106, the conductivity of the graphene layer 106 changes. To this end, the device 100 includes an electrode 110, which is separated or isolated from the metal layer 105 by a gap 111. As a result, the metal layer 105 acts as a second electrode, and a voltage can be applied between the electrode 110 and the metal layer 105, generating an electric field that is approximately parallel to the bilayer 107. Note that the graphene layer 106 is connected to the metal layer 106 and the electrode 110. The conductivity of the graphene layer is high enough for interaction with electromagnetic radiation, but low enough to allow a voltage to develop between the metal layer 105 and the electrode 110. That is, the graphene layer 106 does not exhibit a short circuit that would force the voltage to zero. In some embodiments, the resistance of the graphene layer 106 is in the range of tens of ohms (10-100 Ω). Such behavior may be supported by dislocated graphene sheets that form the graphene layer 106, as opposed to a layer of fully (vertically) connected carbon atoms.

[0060] Graphene is a hexagonal lattice of sp 2 It is a two-dimensional layered sheet of bonded carbon atoms. The carrier dynamics in graphene are governed by intraband electronic transitions described by the Kubo formalism. These result in ultrafast carrier mobilities (up to 200,000 cm at low temperatures). 2 V -1 s -1 ) and silicon (1400cm 2 V -1 s -1 ) is much higher than that observed for the Fermi level E F can be controlled via an external electric field. In this way, the complex conductivity of the graphene film can be tuned with an applied voltage, providing the tunability disclosed herein.

[0061] The term "graphene layer" means that the layer contains graphene, but the graphene layer is not necessarily a single layer of graphene having a single atomic thickness. In that sense, the graphene layer can be a single layer (a single layer of graphene), a few layers (1-100 layers of graphene), or a multilayer (more than 100 layers of graphene). In one embodiment, the graphene layer 106 has about 50 layers of graphene. The above "layers" may be referred to interchangeably as sheets. It should be noted that no substrate or support is included in the device other than the metal layer 105.

[0062] Patterned double layer The bilayer 107 is patterned with a pattern 108 to provide for interaction with electromagnetic radiation by the chip. The pattern can be considered to be an overlapping trench or an array of overlapping trenches. The overlapping trenches can be aligned across the graphene layer and the metal layer by patterning the bilayer simultaneously. In other words, the overlapping trenches are aligned across the boundaries of the metal layer and the graphene layer by patterning the bilayer simultaneously. Each of the one or more trenches extends through the graphene layer and the metal layer to provide interaction with electromagnetic radiation by the chip. The term "trench" is used to refer to a relatively narrow opening in a material or structure with vertical walls and a long dimension that extends through the material or structure. While a trench may be considered as a vertical "cut" in the material, in this disclosure the overlapping trench is not limited to this configuration. In this disclosure the trench can be any shape or design that extends through the bilayer. This can also be considered as a patterning of the bilayer that results in trenches or cuts in the graphene layer and the metal layer, resulting in an overlap as a single design. The trench may also be considered a "slot."

[0063] The patterned bilayer may also define an active or interaction area that is a sub-area of ​​the first surface of the dielectric substrate where interaction with electromagnetic radiation occurs due to the bilayer over the area containing the overlapping trenches.

[0064] As seen at number 109 in Figure 1, the pattern 108 extends through the graphene layer 106 and the metal layer 105. This means that the pattern extends all the way through the bilayer 107 to the dielectric layer (101). As a result, the pattern of the graphene layer 106 and the pattern of the metal layer (105) overlap each other as a single pattern through the bilayer 107. Both the metal layer and the gold layer are patterned only after the formation of the bilayer.

[0065] The term "at least partially" means that the pattern does not have to extend through the bilayer 107 everywhere on the chip 100. In the example of Figure 1, there are essentially three regions: (1) the pattern 108 extends through the entire bilayer 107 where a cross shape is created, (2) at 111 the graphene layer extends above the substrate 101, and (3) the electrode 110 is formed by a separate region of the metal layer.

[0066] It should be noted that the term "pattern" herein generally refers to an area, shape, or geometry in which material is present or absent compared to other areas. This may be accomplished by adding or removing material to those areas. In many embodiments, due to the manufacturing process used, the first step may be to deposit a continuous layer of material, such as a metal / graphene bilayer 107, and then remove material in defined areas to create the "pattern." It should be noted that the term "pattern" does not necessarily relate to something repetitive or regular. On the contrary, a "pattern" may be completely irregular. Typically, a pattern is designed and simulated using computer-aided design (CAD) tools as a physical layout, and then realized using a manufacturing process such as lithography with a mask. In this sense, fabricating a device may include patterning a bilayer through a graphene layer and a metal layer simultaneously in a design that includes one or more overlapping trenches.

[0067] In some embodiments, the pattern includes a periodic 2D array structure, as shown in FIG. 1. This may involve regular repetition of identical structures, such as the Jerusalem Cross of FIG. 1. As a result of such periodic structures, the pattern mimics the atomic structure of the material and its interaction with electromagnetic radiation. However, such materials do not exist in most cases. Thus, in such cases, the patterned bilayer is referred to as a metamaterial.

[0068] Resonator Antenna In essence, the chip 100 presents a dielectric resonator antenna (DRA), where radio waves enter the dielectric layer 101 through the openings of the pattern 108 slots, then bounce back and forth between the reflective layer 104 and the bilayer 107 many times, forming a standing wave. The frequency of that standing wave, and therefore the absorption frequency, is determined by the material properties of the bilayer 107 and the designed metastructure 108. In other words, the thickness of the dielectric layer, together with its dielectric constant, determines the resonator frequency of the designed metastructure. The thickness and dielectric constant of the dielectric layer 101, as well as the material properties of the reflective layer 104, do not change during operation, but the material properties of the bilayer 107 can be tuned by applying a voltage between the graphene layer 106, i.e., the electrode 110 and the metal layer 105, as discussed above.

[0069] adjustment A voltage between the electrode 110 and the metal layer 105 changes the conductivity of the graphene layer 106 and therefore the impedance match of the electromagnetic waves into the chip, changing the resonant behavior. In other words, the device represents an RLC resonant structure, where the graphene layer 106 represents the resistance R, the connector and the metal layer form the inductance L, and the dielectric layer 101 and the ground electrode 104 represent the capacitance C. Applying a voltage between the electrode 110 and the metal layer 105 changes the resistance R. The change in the conductivity of the graphene consequently changes the in-band absorption of the electromagnetic waves and changes the broadband interaction through the device.

[0070] In other words, the device includes a resonant structure including a dielectric layer that is tunable by a voltage applied across the graphene layer, thereby tuning the interaction with electromagnetic radiation. In one embodiment, the resonant structure consists of a dielectric layer sandwiched between two electrodes. The conductivity of the graphene / metal bilayer metasurface is tunable by changing the bias voltage (by changing the voltage applied to the electrodes), changing the resonant characteristics (peak, frequency, Q factor, etc.).

[0071] The electrode 110 may be made of a conductive material, advantageously of the same material as the metal layer 105, such as gold, to simplify manufacturing. In one embodiment, the electrode 110 is separated from the metal layer 105 by an opening 111, such as a trench or a gap. In this sense, the metal layer 105 includes an opening (or a gap) to define a first electrode, which includes one or more trenches for interacting with electromagnetic radiation, and a second electrode for applying a bias voltage. The first electrode corresponds to an electrode that is part of the bilayer and therefore contains a patterning (superimposed trenches). The second electrode, defined by the opening 111, corresponds to the electrode 110. Despite the opening 111 separating the first and second electrodes, the first electrode is connected to the second electrode by the graphene layer 106. This allows a voltage to be applied between the first and second electrodes and parallel to the first surface of the substrate, which allows tuning of the conductivity of the graphene. 1 shows how the bias voltage is applied by circuit 112. Parallel to the first surface means that the vectors of the electric field between the electrodes (the equipotential lines) are approximately parallel to the first surface. That is, as long as the electric field is between two electrodes that are generally side-by-side, there can be a small angle between the electric field vector and the first surface. This is in contrast to an electric field that crosses the first surface, such as the electric field between metal layer 105 and ground electrode 104.

[0072] In one embodiment, because of the openings 111, the graphene layer 106 can be directly attached to the support layer. As a result, the graphene layer 106 is strongly attached to the device because a force (such as van der Waals force) can be established between the graphene and the support layer. Such a force may also be referred to as an adhesion force. This allows the metal layer 105 to be better attached to the support layer because the graphene layer 106 is strongly attached to the device due to the direct attachment to the support layer through the openings 111.

[0073] The openings 111 can be fabricated by forming the metal layer 105 simultaneously with the electrodes 110, with the openings 111 defined by a mask. In one embodiment, the openings 111 can be formed by using a mask on the metal layer and etching the metal layer or by using a directed beam. Using a directed beam, such as a focused ion beam, does not require a mask to create the openings 111. In this embodiment, the openings 111 are created prior to placing an unpatterned graphene layer on the substrate.

[0074] The distance between electrode 110 and metal layer 105, i.e. the width of gap 111, can be very small as long as no discharge occurs from 105 to 110. In some embodiments the distance is 3-4 mm, but can be as small as 100 nm.

[0075] In another embodiment, the electrode 110 may be formed on the graphene layer 106, as opposed to creating a gap by etching the metal layer. A bias voltage may still be created between the electrode 110 and an electrode that forms part of the bilayer used to tune the conductivity of the graphene. This embodiment is also referred to as a voltage parallel to the first surface. In this embodiment, the electrode 110 may be formed by using a mask on the graphene layer and depositing a metal on the device. The metal may be deposited on the device, for example, using a sputtering technique. As a result, the electrode 110 may still be considered as part of a metal layer with a gap that defines a first electrode (part of the metal layer that forms the bilayer) and a second electrode (electrode 110). In this sense, the gap is defined in such a way as to insulate the first electrode and the second electrode from each other. This definition applies equally to the embodiment in which an opening 111 defines the first electrode and the second electrode. In embodiments where the electrode 110 is on top of the graphene layer, the first electrode and the second electrode may overlap vertically, or there may be a horizontal separation between the two electrodes.

[0076] In still further embodiments, two electrodes can be formed on the graphene layer 106, as well as one electrode on each side of the graphene layer 106. However, this embodiment may lead to reduced interaction of electromagnetic radiation with the device, as some electromagnetic radiation is reflected by the metal electrodes arranged on the graphene layer. Such a configuration may also reduce the ability to tune the graphene layer with a bias voltage and may be difficult to fabricate, as the first electrode does not easily adhere to the graphene layer.

[0077] The chip 100 can be tuned with an applied voltage to rapidly change its absorption characteristics, for example, based on a modulation frequency for demodulating received electromagnetic radiation down to baseband to extract data symbols for communication, such as using a QPSK modulation scheme.

[0078] The pattern 108 can be designed to filter desired electromagnetic waves. The size and shape of the pattern can be selected such that waves of a particular polarization or wavelength are transmitted while other waves are reflected off the chip 100. The pattern 108 further determines the directions in which the waves can be transmitted, similar to the principles of slot antennas, and design methodologies from there can now be applied to design pattern 108.

[0079] It has been found that when both the graphene layer 106 and the metal layer 105 are patterned together, the absorption of electromagnetic radiation is significantly increased compared to simply patterning the metal layer 105 and placing a continuous graphene layer without a pattern on top of the metal layer 105. However, first patterning the metal layer 105 and then adding graphene to the pattern so that the same pattern is created in the graphene layer 106 is very difficult to achieve due to the challenging handling properties of graphene. The proposed solution provides a way to result in a patterned bilayer (including a metal layer and a graphene layer) that can be easily replicated in a practical manufacturing process.

[0080] While some of the above examples use a resonant structure with a dielectric layer 101 and a ground electrode 104, other examples may use other effects to realize the interaction with electromagnetic radiation. For example, at higher frequencies above 1 THz, plasmon resonance on the surface of the bilayer 107 may be the main source of interaction, and the dielectric layer 101 and ground electrode 104 may not be necessary. Nevertheless, interactions such as plasmon resonance can still be tuned by applying a voltage across the graphene layer 106. As a result, the full range of applicability of the bilayer may be from 1 GHz to 3 THz, with specific advantages over other approaches in the range of 100 GHz to 3 THz. In other words, the disclosed approach is particularly useful above 100 GHz.

[0081] Attachment area FIG. 2 illustrates a further exemplary chip 200 including a dielectric layer 201 as described above, having a bottom surface 202 and a top surface 203. A reflective conductive layer 204 is also disposed on the bottom surface 202 to reflect electromagnetic radiation and promote resonance. A metal layer 205 is disposed on the top surface 203 and is configured to absorb electromagnetic radiation that is resonating in the dielectric layer 201. A graphene layer 206 is disposed on the metal layer 205 to provide tunability to the resonance and thereby the absorption of the metal layer 205. As described with reference to FIG. 1, the metal layer 205 and the graphene layer 206 form a bilayer 207. In this embodiment of FIG. 2, there is a region 212 where the metal layer 205 does not extend onto the dielectric layer 201. This can be achieved by not depositing metal on the region or by removing the metal from the region after depositing the metal. In some embodiments, the region 212 can be considered an opening in the metal layer 205. In fact, in region 212, dielectric layer 201 is exposed since it is not covered by metal layer 205. As a result, graphene layer 206 covers metal layer 205 and graphene layer 206 extends beyond metal layer 205. As a result, graphene layer 206 is directly attached to dielectric layer 201.

[0082] Physically, this means that the carbon (C) atoms of the graphene layer 206 are in close proximity to the atoms of the dielectric layer. In one embodiment, this proximity is close enough that short-range van der Waals forces attract the graphene layer 206 to the metal layer 201. This is particularly useful for graphene because graphene is a very regular structure, providing a high density of C atoms, each of which exerts an attractive force that would be very weak for a single atom. In one embodiment, the distance between the C atoms and the atoms of the dielectric layer 201 is less than 1 nm, or between 0.6 nm and 0.4 nm.

[0083] Direct attachment to the dielectric layer 201 means that the graphene layer 206 is in direct contact with the dielectric layer, which means that there is no other substance, such as an adhesive, between the graphene layer 206 and the dielectric layer 201. As a result, the graphene layer 206 and the dielectric layer are not inseparable, since the van der Waals forces can be overcome by moving the graphene layer 206 away from the dielectric layer 201. However, this can be reversed and the graphene layer 206 reattached by bringing both layers into direct contact again.

[0084] As a result of the attractive forces between the graphene layer 206 and the dielectric layer 201, the graphene layer 206 is unlikely to peel off from the chip 200. In particular, it is possible to design multiple regions where the graphene layer 206 is directly attached to the dielectric layer 201, and these regions can be distributed across the chip 200. In this way, the graphene layer 206 is attached at multiple points, which provides a reliable mechanical connection of the graphene layer 206. It is noted that the metal layer 206 is conductive, and therefore the van der Waals forces do not provide a significant attractive force. As a result, it has been observed that the graphene peels off the gold surface, which makes subsequent processing almost impossible. The proposed chip provides a solution to that problem by fixing the graphene layer more firmly.

[0085] The resulting bilayer 207 has the advantage of a relatively secure mechanical connection and there is a low risk of the graphene layer 206 peeling off during patterning, making it significantly easier to pattern the bilayer 207. In particular, a pattern such as that shown in Figure 1 can be created on the bilayer 207 that extends through the graphene layer and the metal layer 205 all the way to the dielectric layer 101 to create an absorber of electromagnetic THz radiation.

[0086] FIG. 3 shows yet a further embodiment in which the gaps 111 in the metal layer 305 are used to define exposed areas 312 where the graphene layer 306 is directly attached to the dielectric layer 301, as described with reference to FIG. 1. In that sense, the gaps 111 serve two purposes: as an insulating distance between the electrode 110 and the metal layer 305, and as an "attachment area" for fixing the graphene layer 306 to the dielectric layer 301. By providing additional attachment areas on other sides of the chip, the mechanical attachment can be further improved. In FIG. 3, reference numerals 313, 314 indicate potential boundaries of the metal layer 305, which can be produced by using a mask in a gold sputtering process. If the graphene layer 306 extends over these boundaries 313, 314, the graphene layer 306 is directly attached to the dielectric layer 301. In the embodiment of FIG. 3, the boundaries 313, 314, and therefore the attachment areas, are at the periphery of the chip 200. It is noted that the dielectric layer 301 herein may be significantly larger than the graphene layer and patterns 108 described with reference to Figure 1. As a result, only a very small area of ​​the dielectric layer 301 actively contributes to the absorption of electromagnetic radiation, as defined by the metal layer 305. The graphene layer 306 is then directly attached to the dielectric layer 301 around the metal layer 305.

[0087] There is a third boundary 315 at one end of the chip. However, in this example, the metal layer 305 extends beyond that boundary and beyond the graphene layer 306, so that the metal layer 305 remains exposed. This is useful for adding electrical contacts to the metal layer 305 to apply a bias voltage between the metal layer 305 and the electrode 110 on the other side of the gap 111. In other words, the area where the metal layer 305 is exposed may be referred to as a contact area. It should be noted that there may be a variety of different layouts of the contact and attachment areas. In particular, the contact areas are relatively small, but the attachment areas may be discontinuous and may be interspersed throughout the chip. The different layouts of the attachment and contact areas apply individually and in combination to the chips 100, 200, and 300, as well as to other embodiments.

[0088] Graphene Transfer In one embodiment applied to chips 100, 200, and 300, graphene is first grown separately using chemical vapor deposition and then transferred to the metal layer 305. This can be achieved by using a thermal release tape or by using poly(methyl methacrylate) (PMMA) to transfer the graphene to the metal layer 305. The PMMA method involves spin-coating a layer of PMMA onto the graphene as a support. The metal catalyst on which the graphene grows is then etched away. The PMMA / graphene stack can then be transferred onto the metal layer 305 with the graphene facing the metal layer 305. The PMMA can then be removed by a solvent. Details are described below.

[0089] As an example, a different type of graphene can be used without the method of the previous paragraph. However, if a different graphene type is used, a second electrode may need to be arranged on top of the graphene to apply a bias voltage across the graphene to tune the conductivity. This is in contrast to creating an opening 111 (or gap) to define the second electrode from the metal layer by etching the metal layer.

[0090] Manufacturing method Figure 4 shows a method 400 for manufacturing a chip, such as the chip 100 of Figure 1. This is one example of a method for manufacturing a chip, which is used to explain the main principles of chip manufacturing. However, chip manufacturing is not limited to the exemplary method presented here.

[0091] The chip is fabricated by depositing 401 a metal layer 105 on a dielectric substrate. This can be accomplished by sputtering or thermal evaporation. The metal layer 105 may be shaped to the desired shape, or may advantageously leave some areas of the dielectric layer 101 exposed.

[0092] In one embodiment, a metal stock layer / dielectric substrate configuration may be obtained in which the metal layer does not need to be deposited on the dielectric substrate. Ongoing manufacturing can then be performed on this configuration to obtain a chip. However, placing the metal layer on the dielectric substrate has advantages, such as the metal layer 105 being of a desired shape. Such advantages may be useful for certain uses of the chip. Therefore, it is not always desirable to use a metal stock layer / dielectric substrate configuration to manufacture a chip.

[0093] The next step is to place the graphene layer 106 on the metal layer 105 (402). This forms a bilayer 107 including the metal layer 105 and the graphene layer 106 in the sense that the resonance between the bilayer 107 and the ground electrode 104 can be tuned by applying a voltage to the graphene layer 106. The bilayer 107 is then patterned (403) to provide for the absorption of electromagnetic radiation by the tip. The patterning can be performed with a photoresist (mask) and then an oxygen plasma can be applied to etch the graphene layer 106, followed by an argon etch of the underlying metal layer 105. The photoresist defines the shape of one or more overlapping trenches that form the bilayer pattern. As a result, the pattern extends through the graphene layer 106 and the metal layer 105 down to the dielectric layer 105, at least in part of the pattern. In other words, the bilayer is patterned simultaneously through the graphene layer and the metal layer in a design that includes one or more overlapping trenches. It is important to note that the bilayers are etched together and do not separate during the subsequent etching steps.

[0094] In another example, the graphene layer 106 may be deposited on a dielectric substrate and then the metal layer 105 may be deposited on the graphene layer 106. This configuration still constitutes a bilayer, and the bilayer may be patterned using the methods described herein. In this example, a graphene material layer / dielectric substrate configuration may be obtained in which the graphene layer does not need to be deposited on a dielectric substrate. The metal layer 106 may then be deposited on the graphene layer to form a bilayer, and then patterning of the bilayer may occur.

[0095] As mentioned above, patterning the bilayer involves etching the bilayer, which includes etching the graphene layer with a first etchant and etching the metal layer with a second etchant after etching the graphene layer. In one embodiment, the first etchant and the second etchant are the same etchant. Specifically, the etchant can be a mixture of oxygen plasma and argon plasma. In this sense, the bilayer is patterned simultaneously using a single etchant. Even if the first etchant and the second etchant are different, the process of patterning the bilayer can still be considered simultaneous. For example, if oxygen plasma is used to etch the graphene and argon plasma is used to etch the metal layer, oxygen gas is first introduced into the plasma chamber to hold the chip. After etching the graphene by making the gas into a plasma, oxygen gas is stopped from entering the plasma chamber and argon gas is introduced. This process of patterning the bilayer is considered simultaneous because the chip with the bilayer does not leave the plasma chamber and the mask remains on the chip.

[0096] In another embodiment, the bilayer pattern can also be formed by direct write fabrication methods or lithography techniques, such as focused ion beam (FIB) or laser ablation. In other words, patterning the bilayer includes using a directed beam to create one or more trenches in the graphene and metal layers of the bilayer. In this embodiment, the pattern design is written into the automation control software without the need to use a physical mask.

[0097] Figure 5 shows a method 500 for fabricating a chip, such as the chip 200 of Figure 2 or the chip 300 of Figure 3. The chip is fabricated by disposing (501) a metal layer 205 on a dielectric substrate 201 to provide for absorption of electromagnetic radiation by the chip 200. The dielectric substrate 201 is exposed on a region 212 of the dielectric layer. A graphene layer is then disposed (502) on the metal layer 205, forming a bilayer including the metal layer 205 and the graphene layer 206, with the graphene layer 206 in direct contact with the dielectric layer 201 where the graphene layer 206 extends over the exposed region 212.

[0098] Exemplary Chips This disclosure provides methods for graphene growth, transfer, device fabrication, and characterization. We have implemented a tunable frequency-selective absorber operating at a design frequency of 0.2 THz. The tunability concerns three things: (1) the resonant amplitude of the designed plasmonic mode, (2) frequency tuning of the plasma resonance, and (3) broadband modulation across the entire available range of 0.1-1 THz. Notably, the active region of the device consists of a graphene / gold metasurface bilayer, where the gold exhibits a strong resonant response that is complemented from the solid-state tunability of graphene. An exemplary device is built on a commercially available Rogers 5880 laminate tailored for high frequency communication devices. This disclosure provides the experimental realization of a large-area graphene THz device, where the graphene itself is patterned on the designed metasurface.

[0099] This disclosure can be used to realize a wide range of tunable THz metasurface devices. The presented approach can be adapted to many metasurface designs on many different substrates, enabling widespread applications in THz communications and the development of highly desirable purpose-built reconfigurable THz components.

[0100] Figure 7 shows a schematic diagram of a 0.2 THz metasurface-based resonant absorber featuring a gold thin film pattern consisting of periodically arranged Jerusalem cross slots on a grounded 254 μm thick Rogers 5880LZ substrate. At the first (0.2 THz) resonant mode of the grounded metasurface unit, the absorber is equivalent to an RLC parallel resonant circuit, where the resistance is derived from the dissipative gold film and Rogers substrate with a loss tangent of 2.3 in the 0.2 THz band. The inductance and capacitance are determined by the resonant structure. As a result, the presented design can function as a frequency-selective resonant absorber. The response of this absorber was simulated using finite element method (FEM) analysis.

[0101] The designed Jerusalem cross-slot unit features compact dimensions of 450 μm × 450 μm, which are advantageous for realizing high-quality factor resonance and insensitivity to the angle of incidence of THz radiation. The THz metasurface absorber can be modeled as the equivalent of an RLC resonant circuit, where maximum power absorption occurs at the resonant frequency and the resonant resistance matches well with the wave impedance of the THz radiation. In this case, the equivalent inductance and capacitance are generated from the metasurface structure, while the corresponding resistance is generated from the conductivity of the graphene / gold bilayer and the dissipative properties of the Rogers5880 substrate. To investigate the electromagnetic behavior of the frequency-selective metasurface absorber and optimize its overall performance, detailed three-dimensional full-wave modeling and simulations are performed using the software CST Microwave Studio.

[0102] Within the model, graphene is treated as a surface impedance and quantified through the complex conductivity obtained by THz time-domain spectroscopy (see Methods). The real and imaginary parts of the conductivity in the region of interest (0.1-0.3 THz) were observed to be 37 mS and 10 mS, respectively. Ancillary measurements showed an adjustment of both parts of the complex conductivity of approximately 20%.

[0103] Achieving a good THz absorber device has two aspects, as shown in Figure 7. First, the device is built on a suitable substrate with the desired properties. For this device, the commercially available Rogers 5880LZ Duroid was selected as an ideal candidate with a dielectric constant of 2.2. Second, the graphene film adheres not only to the Rogers stack but also to the gold regions of the metasurface and electrical contacts. This can be problematic since graphene is notoriously difficult to adhere to gold. A suitable film was successfully transferred to the Rogers 5880 / gold base structure. The graphene film is at least 3 cm x 3 cm in size, highly uniform (minimal wrinkles) and free of voids / defects. Wrinkling of the film or void defects can lead to device failure in subsequent fabrication steps.

[0104] Successful direct transfer of graphene films onto gold and Rogers substrates allowed metasurface regions (see FIG. 7) to be patterned directly onto both gold and graphene. Such fabrication approach and bilayer metasurface design enabled functional devices with advantageous properties. By patterning gold and graphene bilayers together, the gold portion supports most of the plasmon resonance activity, while the graphene provides tunability to the device. Such tuning is also achieved without the need for dielectric layers to build fields, or gate electrodes, both of which are detrimental to device performance.

[0105] Moreover, the bilayer results surpass those of the gold and graphene metasurfaces considered separately. Without graphene, the gold is not tunable, and without gold, the graphene does not support plasmonic resonances. A good bilayer is also important for such devices, since adding a dielectric layer or adding an unpatterned graphene film would be difficult. It was observed that the THz field with a dielectric on top of the gold screen completely damped the resonant behavior, even with the addition of a complete graphene sheet on the gold metasurface. In fact, no evidence of plasmonic modes could be observed for the gold metasurface with a complete graphene sheet transferred on top.

[0106] Interestingly, in adapting the gold metasurface to a bilayer, all resonant modes between 0.1 and 0.6 THz were addressed in the device. This is detailed in Figure 2(c). Importantly, this includes the fundamental 0.2 THz absorbance for which the device was designed. The frequency of each mode was very slightly shifted and the intensity of the modes increased. Higher order modes above 0.6 THz, present in the gold metasurface, are suppressed in the bilayer structure. However, these are well away from the region of interest for which the structure was designed.

[0107] Despite these changes in the frequency and amplitude of the modes, the bilayer metasurface now allows a high degree of tunability of the strength of the modes, their resonant energies, and the overall broadband modulation. To analyze the tunability of the selective absorber, the device is 11 The device is assumed to contain a single port with the parameters: 11 For the parameters, the ratio of reflected to incident electromagnetic power can be obtained directly through the power spectrum measured in a time-domain spectroscopy setup. This process is detailed in the Methods section.

[0108] Figure 1(c) shows the device S for applied voltages from 0 to 6 V. 11parameters are given. In the transition from the gold metasurface to the gold / graphene bilayer, the overall resonant behavior of the structure remains.

[0109] The inclusion of the graphene metasurface decreased the resonant frequency by 0.01 THz and increased the loss to 18 dB. Such a small shift in frequency is significant considering the relative difference in the conductivity of the gold and graphene layers. Thus, careful fabrication of the bilayer structure can support desired properties of gold-only devices, with the added ability to tune from the graphene inclusion.

[0110] With increasing voltage, the device shows clear tunability: first, a broadband response of 5 dB is reflected in the peak shoulder; second, there is an enhancement of the resonant mode of 7 dB (the total change of 12 dB is the sum of both effects); and third, there is a systematic frequency tuning of 0.05 THz over the voltage range of 0-6 V.

[0111] The complete voltage dependence of the device performance is further detailed in Figure 2(a) and (b), where we reveal the nonlinear device response. For voltages from 0 to 3 V, the peak position, S 11 Little or no systematic changes are observed in any of the parameters, FWHM or peak area. However, from 3 to 6 V, the peak position shifts from 0.192 THz to 0.187 THz, the S11 parameter from -18 dB to -25 dB, the FWHM from 0.017 THz to 0.010 THz, and the peak area from 0.47 to 0.38. It should be noted that the S-parameters presented in Figure 2(b) are consistent with the omitted broadband response. Thus, they reflect a direct enhancement of the resonant modes, independent of any broader frequency effects. Thus, the total change in peak intensity shown in Figure 1 is dominated by the dual response from the graphene part, i.e., a broadband modulation of 5-6 dB and a direct enhancement of the resonance amplitude of 7 dB. Thus, it can be concluded that there is a direct amplification of the designed plasmonic resonance, rather than a simple reduction of the signal from broadband graphene absorption.

[0112] Interestingly, the FWHM exhibits a stronger reduction (37.5%) than the peak area (21.2%) over the voltage range. This is reflected in the improvement of the Q-factor of the mode, which increases from 11.8 to 18.7 at 6 V applied. Thus, biased graphene has the effect of reducing the energy lost within the resonant mode. Biased graphene not only amplifies the absorption band, but also reduces its bandwidth improving its quality.

[0113] The frequency tuning of the device also follows a nonlinear characteristic: the resonant frequency remains consistent up to above 3 V, where a shift to lower photon energies is observed. Compared to the 0 V resonant frequency at 0.191 THz, the total shift over a 6 V applied voltage is 5 GHz, i.e., 2.5%.

[0114] It should be noted that the bilayer characterization was repeated with the polarity reversed (second panel of Figure 10). Furthermore, for voltages above 6 V, the device was observed to degrade. Details of this, along with comprehensive data for all resonant modes observed from 0.1 to 0.6 THz, are provided in the ESI.

[0115] Wideband Modulator Superimposed on the resonant modes is a broadband modulation of the THz waveform. This is evident across the entire available spectrum, shown in Figure 7. The asymptotic shape of the curves at 0.19 THz and 0.56 THz arises from the relative shift of the resonant modes with the change in voltage. Although the modulation is unclear in these regions, it provides experimental verification of the tunability of the frequency of the bilayer. This effect is also present to a lesser extent for the 0.36 THz and 0.40 THz resonances. Such behavior invites the use of the bilayer as a THz modulator.

[0116] There are three transmission windows: 0.23-0.32 THz, 0.43-0.50 THz, and 0.72-1 THz. In the former, the modulation depth is

[0117]

number

[0118] is defined as , and is between 80 and 90%. In the 0.43-0.50 THz window, it increases to 90-93%. From 0.72 THz to 1 THz, the modulation depth varies from 94% to 96%, which is extraordinary in the absence of a dielectric between the graphene and metal layers and at such low applied voltages. The full frequency characteristic of the modulation depth at 6.2 V is shown in Figure 8. There is an overall frequency dependence in the modulation behavior of the bilayer; that is, the modulation depth increases with the photon energy. In the presented range (at 6.2 V), the modulation depth is 65% at 0.1 THz, increases steadily to 90% at 0.31 THz and remains above 95% for frequencies above 0.73 THz. Due to the interruption of the spectrum close to the plasma resonance frequency, arising from the frequency tuning characteristics, it is difficult to ascertain a mathematical relationship between the modulation depth and frequency over the full range at this voltage.

[0119] Synthesis and characterization of graphene Graphene films are produced using a nickel-catalyzed CVD process (99% purity, annealed). The process includes an initial vacuum step to produce higher quality graphene films, and lineol acid dissolved in ethanol (60% v / v) is replaced with soybean oil.

[0120] In one example, the following graphene production protocol may be used. 1. A 15 cm x 12 cm piece of nickel foil (99% purity, annealed) is cleaned with IPA and then rolled into a cylinder with the 12 cm lengths touching on opposite sides. 2. Load two ceramic boats (3*3*0.2 cm) with 60 μL of lineolic acid (60% in ethanol). 3. The boat and foil are loaded into a 50 mm ID tube furnace reactor with a 30 cm hot zone and oriented so that the boat is on either side of the foil with a 1 cm gap, and the foil is aligned in the center of the hot zone. 4. The furnace is then sealed. 5. The furnace is heated to 150° C. and the tube is evacuated to a base pressure of 50 mTorr. 6. Close the vacuum and hold the temperature for 5 minutes. 7.Then the vacuum line is opened and the pressure is returned to 50 mTorr. 8. The vacuum is then closed and the furnace is brought to 950°C. 9. The temperature is then held for 2 minutes. 10. Once the time is up, turn off the furnace and open the vacuum. 11. Once the temperature reaches 850°C, the tube is shifted out of the furnace so that the area of ​​the tube containing the foil is now exposed to the outside air rather than the furnace hot zone. 12. Leave the sample to cool to room temperature. 13. Once at room temperature, close the vacuum line and return the tube to atmospheric pressure. 14. The tube is then opened and the foil removed. 15. Nickel foil is now coated with a thin graphene-like film.

[0121] In a further embodiment, the following transcription protocol may be used. 1. Graphene sheets are cut to the desired size, 25 x 25 mm. 2. PMMA 950K Mw dissolved in anisole (5 g / L) is then spin coated onto the foil. 3. The rotation speed used is 2000 rpm. 4. Once coated, allow the samples to dry for 24 hours. 5. Once dry, trim the edges of the coated foil by approximately 500 μm. 6. The foil is then soaked in 0.5M FeCl 3 The semiconductor device is then aligned in an etching solution of 1000 μm. 7. Leave the sample for 24 hours. 8. Once the nickel has dissolved, the PMMA coated graphene film is transferred into clean DI water. 9. From here it can be transferred and used to create a device.

[0122] In still further examples, graphene may be produced as described in WO 2017 / 027908 or WO 2018 / 161116, it being noted that other methods of making graphene and their results may be used.

[0123] Terahertz characterization of the graphene film was performed on a fiber-coupled Batop time-domain spectroscopy (TDS) system in transmission configuration. A photoconductive antenna (PCA) was utilized for both THz production and photodetection. The graphene film was transferred onto a PTFE substrate for characterization. The substrate was designed to be 3 mm thick to achieve an optimal tradeoff between the measurement signal and avoiding back reflection of the time-domain signal. The complex conductivity of the graphene film is extracted, followed by the scattering rate, carrier mobility, and carrier density. From the THz-TDS, the carrier mobility and carrier density are found to be 1393 cm, respectively. 2 V -1 S -1 and 17 x 10 13 cm -2 These are obtained from a dc conductivity of 37 mS and a scattering time of 209 fs (scattering rate 0.76 THz).

[0124] Fabrication of graphene / gold bilayer devices A commercially available 0.254 mm thick Rogers 5880LZ laminate was used as the device substrate. The ground plane was prepared with a 220 nm sputtered gold film. The front side underwent the same gold deposition with a hard mask to define the metasurface bilayer and contact areas. After deposition, the front side was treated with argon reactive ion etching at 30 W for 1 min. A nickel / graphene foil (25 mm × 25 mm) was spin-coated with poly(methyl methacrylate) (PMMA) polymer. The nickel foil was then coated with FeCl 3 The graphene / PMMA structure was then transferred onto a previously prepared Rogers substrate. Finally, the PMMA was dissolved in anisole and the sample was dried. The graphene film was then transferred onto the Rogers laminate using a wet transfer technique.

[0125] The graphene / gold bilayer pattern was realized using standard photolithography procedures, i.e., spin-coating photoresist, UV light exposure, and photoresist development. The patterned device chip with the photomask protection layer was then etched using a novel reactive ion etching process. First, O was used to remove the unprotected graphene. 2 Remove the unprotected gold layer by etching with Ar (a chemically inert gas) followed by a short final O 2 Plasma etching was applied to clean the device chip. Electrical connections of external wires to the gold contacts of the metasurface were made using silver epoxy. 2 Although a plasma is used to etch the graphene and an Ar plasma is used to etch the gold layer, the disclosed method is not limited to these plasmas. It should be noted that any combination of chemically reactive and chemically inert gases is sufficient to pattern the device chip.

[0126] Terahertz characterization of double-layer metasurfaces Terahertz (THz) characterization of the device was performed on a fiber-coupled Batop time-domain spectroscopy (TDS) system in a reflection configuration. A photoconductive antenna (PCA) was utilized for both THz generation and photodetection. To quantify the absorber performance, the reflected power of electromagnetic waves from the metasurface device was

[0127]

number

[0128] (The reflected power of the electromagnetic wave is

[0129]

number

[0130] ) are compared with a reference measurement (

[0131]

number

[0132] ) is compared to the absorber, which is expressed by the relation S 11 = 10log(R), the corresponding S 11 It is considered to be a single port device with the parameters: where R is the ratio (reflectance) of the sample and reference power spectra,

[0133]

number

[0134] It is.

[0135] Tunable performance at 0.2 THz THz-time domain spectroscopy is used to study the performance of the absorber (the measurement setup is shown in Figure 6). In the reflection configuration, the reflected THz power (electromagnetic wave after interacting with the device) is 11 -parameter, equivalent as a ratio to the incident THz beam (electromagnetic wave before interacting with the device). In this way, the actual performance of the absorber can be directly compared to the theoretically modeled response in CST (Figure 17).

[0136] Figure 17a shows the experimental frequency response of the graphene / gold bilayer metasurface compared to the same design with a gold-only metasurface layer. A high-quality resonance at 0.2 THz is generated in both cases, and the simulated S calculated using CST is presented in Figure 17b. 11 The very good agreement between the experimental and simulation results confirms the validity of the design and experimental implementation of the novel graphene / gold bilayer metasurface device.

[0137] Figure 12 shows the THz power ratio S of the absorber at the 0.2 THz resonance designed with applied voltages from 0 to 6 V. 11 We show that with increasing voltage, systematic tunability of the device's resonance amplitude and frequency is displayed. First, there is a 16 dB change in signal power at resonance, significantly stronger than previously outlined reports for THz metamaterials tuned through graphene. Furthermore, there is a phase shift observed as 5 GHz of frequency tuning over an applied 0-6 V. Tuning is achieved at very low voltages (0-6 V) using a simple biasing scheme, which compares favorably to what has been reported in the literature, which use more complex gate electrode schemes and typically much higher bias voltages.

[0138] The voltage dependence of the device tunability is shown in Figure 13. Interestingly, the voltage dependence is nonlinear. For voltages from 0 to 3 V, little change is observed in either the resonance peak position or amplitude. However, from 3 V to 6 V the change becomes more drastic, with the resonance position shifting from 0.192 THz to 0.187 THz and the power amplitude from -18 dB to -25 dB. Also, the resonance FWHM decreases from 0.017 THz to 0.010 THz and the corresponding area decreases from 0.47 to 0.38. This reflects an increase in the resonance Q factor from 12 to 19 with applied voltage.

[0139] The tuning mechanism of the absorber is due to two main effects, both of which depend on the graphene in the bilayer. First, the tuned graphene conductivity changes the equivalent resistance (R) of the bilayer in the RLC resonant circuit model, and therefore changes both the resonant frequency and amplitude. In other words, the tuning changes the impedance matching of the 0.2 THz radiation to the metamaterial resonator structure, which affects the resonant frequency and the maximum power absorption at the resonant frequency. With increasing voltage, the improved impedance matching of the device leads to a stronger resonance of 7 dB at 0.2 THz, as well as a frequency shift of 5 GHz. Similarly, the improved matching condition is verified through an increase in the Q factor of the 0.2 THz mode.

[0140] Second, the broadband absorption of the incident THz waveform is tuned through a change in the Fermi level of graphene and therefore in its intraband conductivity. This is experimentally demonstrated by a 9 dB signal power drop adjacent to the resonance peak (outside the resonance frequency) with increasing voltage. Such an effect is also observed in the broader THz spectrum, as will be discussed in the next section. The total 16 dB amplitude and 5 GHz frequency tunability, detailed in Figure 13, is a superposition of the two effects mentioned above.

[0141] Broadband operation up to 1 THz Apart from the designed 0.2 THz resonance, the device presents an interesting broadband response. A series of auxiliary modes are found at 0.36 THz, 0.40 THz, and 0.56 THz, as can be seen in Figure 14 (right panel). These modes are also observed in the gold-only device and are therefore due to the resonant circuit design. Similar to the 0.2 THz feature, these resonances also exhibit significant amplitude and frequency tunability with applied voltage. However, this tuning is less pronounced than that at the 0.2 THz resonance peak. A summary of each resonance and its behavior at applied 0 V and 6 V can be found in Table 1.

[0142] [Table 1]

[0143] There is a broadband modulation of the THz waveform superimposed on the resonant mode. This is evident across the entire available spectrum, shown in Figure 16. Three transmission windows exist: 0.23-0.32 THz, 0.43-0.50 THz, and 0.72-1 THz. In the former, the modulation depth is

[0144]

number

[0145] , which is defined as , is between 80% and 90%. In the 0.43-0.50 THz window, it increases to 90%-93%. From 0.72 THz to 1 THz, the modulation depth varies from 94% to 96%. As can be seen in Figure 16, there is an overall frequency dependence in the modulation behavior of the bilayer; i.e., the modulation depth increases with photon energy. The observation of an effective tuning effect across the entire measured THz frequency band validates that the bilayer design can be adapted to tunable metamaterial devices covering the entire 0.1-1 THz range. This is expected to apply to similar structures operating beyond 1 THz.

[0146] Graphene ET122-124 Fabrication Protocol The following description provides further details regarding the fabrication of the graphene layers 106 / 206 / 306.

[0147] First, a piece of nickel foil (99% purity, annealed) 15 cm x 12 cm is washed with IPA and then rolled into a cylinder with the 12 cm length touching on opposite sides. Next, two ceramic boats (3*3*0.2 cm) are loaded with 60 μL of lineolic acid (60% in ethanol). The boats and foils are loaded into a 50 mm inner diameter tube furnace reactor with a 30 cm hot zone, oriented so that the boats are on either side of the foil with a 1 cm gap, and the foil is aligned in the center of the hot zone.

[0148] The furnace is then sealed and heated to 150° C. and the tube is evacuated to a base pressure of 50 mTorr. The vacuum is then closed and the temperature is held for 5 minutes.

[0149] The vacuum line is then opened and the pressure is returned to 50 mTorr. The vacuum is then closed and the furnace is brought to 950° C. The temperature is then held for 2 minutes. After this time the furnace is switched off and the vacuum is opened.

[0150] Once the temperature reaches 850°C, the tube is shifted out of the furnace so that the area of ​​the tube containing the foil is exposed to the outside air rather than the hot zone of the furnace. The sample is then left to cool to room temperature.

[0151] Once at room temperature, the vacuum line is closed and the tube is returned to atmospheric pressure. The tube is then opened and the foil is removed. The nickel foil is now coated with a thin graphene-like film.

[0152] Transcription protocol The following description provides further details regarding the transfer of graphene onto the metal layer 105. The graphene sheets prepared according to the above method are cut to the desired size, such as 25 mm x 25 mm. PMMA 950K Mw is then dissolved in anisole (5 g / L) and spin-coated onto the foil. The spin speed used may be 2000 rpm.

[0153] After spinning, the coated sample is allowed to dry for 24 hours. Once dry, the edges of the coated foil are trimmed by approximately 500 μm. The foil is then immersed in 0.5 M FeCl dissolved in water. 3 The samples are then left for 24 hours. Once the nickel has dissolved, the PMMA-coated graphene film is transferred to clean DI water, from where it can be transferred and used to create devices.

[0154] overview This disclosure provides a highly tunable THz frequency selective absorber based graphene / gold bilayer metasurface structure. The bilayer design was developed through a holistic experimental approach covering theoretical modeling and optimization followed by graphene fabrication, transfer, device patterning, and characterization. A benchmark resonant Q value of 19 (at 6 V applied) is observed for the designed 0.2 THz frequency selective absorber along with 16 dB large amplitude tuning and 5 GHz frequency tuning. The device behaves as expected from simulations proving that the bilayer implementation provides a predictable response. This is useful for the fabrication of commercially viable and scalable electronic devices.

[0155] In addition, higher order resonant modes are revealed at 0.36 THz, 0.40 THz, and 0.56 THz, and also exhibit amplitude and frequency tunability up to 1 THz, with broadband modulation consistently exceeding 90%. Successful experimental implementation of the graphene / gold bilayer device offers the opportunity to realize a variety of impactful tunable, flexible, reconfigurable, and programmable THz metamaterial devices.

[0156] The observed tuning effect can be attributed to two main mechanisms. First, the change in the conductivity of the voltage-biased graphene / gold bilayer (top electrode) changes the impedance match of the resonant structure to the wave impedance of the THz radiation, and therefore changes the resonant frequency and its amplitude, as predicted by the RLC resonant circuit model. Second, the change in the graphene surface conductivity changes the graphene's intraband absorption of the THz radiation. This is confirmed by the tuning effect observed across the entire measured THz band, including the resonant peak and the non-resonant region. The first mechanism, based on the RLC resonator effect, is more dominant towards the lower frequency side (stronger change at 0.2 THz than the other peaks), while the second effect of the graphene's intraband THz absorption becomes stronger towards the higher THz frequency band, and the broadband amplitude modulation increases at higher frequencies, as shown in Figure 16.

[0157] Because the device is built on flexible commercial radio frequency stacks, it can potentially be implemented in practical THz electronic circuits and flexible electronics. The graphene / gold bilayer archetype can be readily adapted to the many numerically modeled metamaterial structures currently in the literature for tunable THz electronic devices.

[0158] It will be understood by those skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments without departing from the broad general scope of the present disclosure, and the present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

Claims

1. 1. A method for manufacturing a device, the method comprising: disposing an unpatterned graphene layer on a substrate including an unpatterned metal layer to form an unpatterned graphene-metal bilayer attached to a surface of the substrate; patterning the bilayer through the graphene layer and the metal layer in a design including one or more overlapping trenches; each of the one or more trenches extends through the graphene layer and the metal layer to provide for interaction with electromagnetic radiation; The method further includes creating a gap in the metal layer to define a first electrode and a second electrode.

2. 2. The method of claim 1 , wherein the patterning is performed using a single mask that defines the design, thereby creating the trenches through the graphene layer and the metal layer in a single patterning step.

3. 3. The method of claim 2, wherein the method further comprises using the single mask to perform both an etch of the graphene layer and an etch of the metal layer.

4. The method further comprising: Etching the graphene layer with a first etchant; 4. The method of claim 3, further comprising: after etching the graphene layer, etching the metal layer with a second etchant.

5. The method of any one of claims 1 to 4, wherein the method further comprises disposing the unpatterned metal layer on the substrate.

6. The method of any one of claims 1 to 5, wherein the gap is created prior to disposing the unpatterned graphene layer on the substrate.

7. 7. The method of claim 1, wherein patterning the bilayer comprises creating the one or more trenches in the graphene and metal layers of the bilayer using a directed beam.

8. A device, comprising: a support layer having a first surface; a patterned graphene-metal bilayer comprising a metal layer deposited on the first surface and a graphene layer deposited on the metal layer, the bilayer including one or more overlapping trenches extending through the graphene layer and the metal layer to provide for interaction with electromagnetic radiation; the overlapping trenches are aligned across the graphene layer and the metal layer by patterning the bilayer; the metal layer includes a gap to define a first electrode including the one or more overlapping trenches and a second electrode; the first electrode is connected to the second electrode by the graphene layer to provide tunability by varying a voltage applied between the first and second electrodes and across the graphene layer parallel to the first surface.

9. The device of claim 8 , wherein the second electrode is on top of the graphene.

10. the one or more trenches define an array; The device of claim 8 or 9, wherein the array extends across the bilayer.

11. The device of claim 10 , wherein the array is a periodic design to provide for the interaction, e.g., metamaterial structure interaction, with electromagnetic radiation by the device.

12. The support layer is a dielectric layer, Optionally, the device comprises a resonant structure including the dielectric layer, the resonant structure being tunable by the voltage applied across the graphene layer, thereby tuning the interaction with the electromagnetic radiation.

13. the dielectric layer having a second surface opposite the first surface; 13. The device of claim 12, wherein the device further comprises a reflective conductive layer disposed on the second surface to reflect electromagnetic radiation propagated through the dielectric layer back to the dielectric layer to create a resonance within the dielectric layer.

14. 14. The device of claim 8, wherein the electromagnetic radiation has at least one of the following frequencies: 1 GHz to 3 THz, 100 GHz to 3 THz, and greater than 100 GHz.

15. the graphene layer extends beyond the metal layer and is directly attached to the support layer; Optionally, the graphene layer comprises: the gap between the first electrode and the second electrode; and A device according to any one of claims 8 to 14, wherein the metal layer is directly attached to the support layer in one or more of its peripheral regions.

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