Metal-insulator-metal tunnelling diode for operation in the visible or infrared spectrum

Abstract

Disclosed is a diode device (1) including an insulator (7) extending between and in contact with two metal terminals (3, 5), wherein the insulator comprises at least one epsilon-near-zero (ENZ) material, or comprises at least one epsilon-negative (ENG) material (7A) and a second insulator material (7B) forming a double insulator structure, and an electron source layer (9), particularly of graphene, between a metal terminal and the ENZ or ENG material. The insulator provides a reduced effective capacitance which permits rectifying diode operation at THz, infrared or visible frequencies, particularly for a solar radiation rectenna.

Description

[0001] METAL-INSULATOR-METAL TUNNELLING DIODE FOR OPERATION IN THE VISIBLE OR INFRARED SPECTRUM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a diode, a diode device, a rectenna diode device, and an optical rectenna diode device, and to a rectenna or solar cell including the diode, diode device, the rectenna diode device, or the optical rectenna diode device.

[0004] BACKGROUND

[0005] The sun is a major energy source for us and has been fulfilling our planet's energy needs in various direct and indirect ways.

[0006] Historically, solar energy harvesting has been expensive and relatively inefficient. New technological advances and sustainable environment ambition towards a net-zero target have attracted many governments and industries interested in using renewable energy, especially solar energy.

[0007] Solar cells, which are made from silicon, can convert, in theory, about 32% and, in practice, only 23% of the available light energy into electrical energy.

[0008] To outpace current solar cell technology, a new approach is needed to capture more energy from solar radiation whilst being less expensive to manufacture and set up compared to the state-of- the-art designs.

[0009] Several industries would be eager to adopt solar power if the conversion efficiency is enhanced and the size / cost is reduced. Amongst such industries are satellite and terrestrial mobile / wireless communication industries as energy consumption, a major cost component in network operational cost, is rising with 5G and future 6G and is essential in meeting their commitment to a sustainable environment.

[0010] Traditional photovoltaic (P.V.) solar technologies, such as the typical silicon solar cell, can only capture a small fraction of the available solar energy. This limitation is due to the intrinsic material properties of silicon. Much of the ultraviolet and near-infrared radiation is not efficiently harvested (See Figure 1A). In the search for an alternative material, scientists have harnessed the tunability of perovskites to create semiconductors with properties similar to silicon. The Perovskites have a broad absorption spectrum, fast charge separation, long transport distance of electrons and holes, and an extended carrier separation lifetime, making them a very effective solar material. Although they are very efficient at absorbing high-energy photons in the ultraviolet and visible spectrum, their absorption quickly drops off at 780 nm, making perovskites essentially transparent to the near-infrared spectrum where more than half of the total available energy is located.

[0011] Today, the highest achievable efficiency of any solar panel is around 23%. Infrared radiation, representing more than half of the solar radiation spectrum, is not captured by most photovoltaic devices.

[0012] Therefore, there is a pressing need to harvest this source of longer wavelength energy using alternative harvesting techniques. To address this demand, several approaches have been studied and developed in recent years, including tandem and multi-junction structures. These structures suffer from the complex structure, sophisticated fabrication process, and lack of rare materials that directly lead to elevating the cost of the cell.

[0013] This makes the silicon-based P.V. cells still the only available technology that could be employed in low-cost commercial applications.

[0014] One such alternative energy harvesting technique that has emerged is based on rectennas.

[0015] A rectenna is an antenna coupled to a rectifying diode (See Figure 1 B). A diode is a two-terminal electronic component that conducts the electric current in one direction while blocking it in the opposite direction. This behavior is called rectification and converts alternating current (A.C.) to direct current (D.C.).

[0016] However, due to their nonlinear current-voltage characteristics, diodes can have more complicated behavior. The nonlinear behavior of a semiconductor diode can be tailored to perform different and various functions by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacturing. These techniques are used to create specialpurpose diodes that perform many different functions: to regulate voltage, to electronically tune varactors, and to implement oscillators, amplifiers, mixers, modulators / demodulators, and other electronic and communication circuits. The diode is usually modelled as a resistor in parallel with a capacitor. The value of the capacitor sets the diode cutoff frequency. The state-of-the-art work has been able to produce high-speed diodes with a cutoff frequency of up to 5 TeraHertz (THz) using solid-state technology [1] and [2], Introducing high-speed THz diodes enables a large number of applications in society, such as remote sensing / radiometers for environmental monitoring (space-borne and terrestrial), security and industrial radars, inspection, food quality, medicine, pharmaceutical industry, and high- resolution car radars.

[0017] One exemplary promising application of the diode is in energy harvesting systems. In principle, rectennas are high-efficiency devices that transform infrared / visible radiation into D.C. output currents. In contrast to the P.V. solar cells, the rectennas can theoretically capture solar energy with an efficiency (q) of almost 100%.

[0018] For high-efficiency rectennas, high diode responsivity is required. A diode's responsivity is defined as the ratio of the D.C. output current to the A.C. power arriving at a diode's terminals. The conventional p-n junction and Schottky diodes have not successfully introduced efficient rectennas [3]. A tunnel diode with a single insulator layer typically does not give a high zero-bias responsivity. However, multiple insulator layers with different bandgaps and electron affinities can improve the diode's nonlinear behavior and, accordingly, attain higher responsivity. A rectenna has many applications in industries like solar power satellites, battery-less devices, RFID tags, proximity cards, and contactless smart cards employed in the Internet of Things (loT) and 5G, most likely for 6G wireless communications.

[0019] Figure 2 summarizes the results of a comprehensive survey on available technologies that can be used for solar energy harvesting. These technologies can be broadly classified into several main groups based on their underlying principles of operation.

[0020] The first group includes the geometrical (ballistic) diodes that utilize the geometric properties of semiconductors to achieve rectification [4]-[6] . The second group is the photon-assisted tunnelling (PAT) diodes that are based on the principle of quantum tunnelling and rely on the absorption of photons for their operation [7]-

[0010] . The third group is the point contact diodes composed of a sharp metal tip and a semiconductor

[0011] -

[0013] . The graphene diodes

[0014]

[0015] , Oxygen-non-stoichiometry-controlled homo-interface diodes

[0016]

[0017] , metal-insulator-metal (MIM & MUM) diodes

[0018] -

[0026] , Carbon Nanotube (CNT) diodes

[0027] -

[0029] , and plasmonic diodes

[0030] are the other available approaches that have been introduced before.

[0021] However, despite their potential, some technologies still face limitations. For instance, CNTs MIM diodes suffer from low photon-to-electron conversion efficiency or the inability to provide highspeed switching for visible and optical frequencies (Schottky diodes, point contact diodes, geometrical diodes, PAT diodes, metal-insulator-metal (MIM) diodes).

[0022] Graphene diodes offer several advantages in solar energy harvesting due to their high electron mobility and unique electronic properties. These features enable excellent high-speed performance, important for achieving optimal or significant energy conversion. Similarly, Oxygen- non-stoichiometry-controlled homo-interface diodes possess potential for high-efficiency solar energy harvesting, as they enable the precise control of oxygen stoichiometry at the interface, leading to improved performance.

[0023] Numerous research efforts have been carried out to address the challenges associated with improving the efficiency and cutoff frequency of diodes during the last decade. However, despite these efforts, both of these issues remain unresolved. As a result, there is a significant gap between the efficiency level achieved by current solar cell technology and the efficiency level of empirical nano-rectennas. Despite ongoing research in this area, there is still much work to be done to improve the performance of diodes and bridge this gap in efficiency.

[0024] In order to address these issues, the Inventors considered it to be imperative to delve deeper into the technology of rectennas to conduct further analysis to better understand the underlying mechanisms and factors that impact the performance of these devices. By gaining a more comprehensive understanding of rectenna technology, it may be possible to identify new approaches and strategies for overcoming the challenges associated with improving diode efficiency and cutoff frequency. Additionally, continued investigation in this area could lead to the development of more advanced and sophisticated diodes and rectenna designs capable of achieving even greater efficiency and performance. In contrast to the antenna that has a good radiation efficiency performance (nrad), the key component of a rectenna which usually degrades harvesting efficiency (n =T]radxTid / ode) is the rectifying diode (r|dfode).

[0025] Two main difficulties that significantly limit the performance of rectennas at high frequencies are (i) the extra-large value of the capacitor of the rectifying diode and (ii) the efficiency of the electron tunnelling in an ordinary material.

[0026] To overcome the low efficiency of quantum tunnelling (rid / oc / e), some researchers have utilized a 1D graphene layer to provide an infinite source of electrons during the tunnelling process

[0031] -

[0033] . These efforts are in good agreement with those reported previously

[0014] and

[0015] .

[0027] Some researchers have addressed the extra-large value of a parasitic capacitor by using a material with negative electron affinity (NEA)

[0034] , The state-of-the-art work has addressed low cutoff frequency leading to high-speed diodes with a cutoff frequency of up to infrared frequencies. Still, the problem has remained unsolved for visible applications. The limits of materials with negative electron affinity and the instability of NEA materials at room temperature have resulted in the inability to have efficient, high-frequency diodes. Incorporating an artificial inductor to load the diode is a new approach recently suggested to increase the diode cutoff frequency. It allows more effective capturing and converting of the infrared and visible spectrum to electric power

[0035] .

[0028] SUMMARY

[0029] A goal of the invention of the present disclosure is to provide a solution to the previously mentioned difficulties and inconveniences.

[0030] A goal of the invention of the present disclosure aims to provide a solution to the previously mentioned difficulties limiting the performance of rectennas at high frequencies which are the high capacitor / capacitance value of the of the rectifying diode and the electron tunnelling efficiency.

[0031] It is a further goal to address the problem of providing high-speed diodes with a cutoff frequency suitable for visible spectrum applications.

[0032] The aim of the present disclosure is furthermore to provide innovative electronics for new and efficient solar cell structures that work at the visible-infrared frequency spectrum. The present disclosure aims to provide an efficient diode and a broadband covering visible / infrared diode with a highly asymmetrical response and non-linearity, as well as a novel broadband rectenna for solar energy harvesting.

[0033] It is therefore one aspect of the present disclosure to provide a device or diode device including a first metal terminal and a second metal terminal; at least one insulator extending between the first and second metal terminals and in contact with the first and second metal terminals; wherein the at least one insulator may comprise or consist solely of at least one epsilon-near-zero (ENZ) metamaterial or material, a permittivity of the at least one insulator being defined by the at least one epsilon-near-zero metamaterial or material to provide an intrinsic diode capacitance permitting an operation frequency in a visible or infrared frequency spectrum; or the at least one insulator may comprise or consist solely of at least one epsilon-negative (ENG) metamaterial or material forming, with a second insulator material, at least one double insulator structure, wherein the at least one epsilon-negative (ENG) metamaterial or material is configured to provide a negative capacitance and an effective intrinsic capacitance value of the at least one double insulator structure permitting an operation frequency in a visible or infrared frequency spectrum, and wherein the diode device may include at least one electron source layer extending between the first and second metal terminals and in contact with the at least one epsilon-near-zero (ENZ) metamaterial or material or the at least one epsilon-negative (ENG) metamaterial or material.

[0034] It is a further aspect of the present disclosure to provide a visible-infrared rectenna including at least one antenna or nano-antenna and the at least one diode device, the at least one diode device being coupled to the at least one nano-antenna to rectify, to direct current (DC), an alternating current or voltage provided by the at least one nano-antenna during visible and / or infrared electromagnetic radiation capture by the at least one nano-antenna.

[0035] It is a further aspect of the present disclosure to provide a visible-infrared spectrum solar cell including at least one or a plurality of the diode devices or the visible-infrared rectenna.

[0036] Particular embodiments of the diode device, the visible-infrared rectenna and visible-infrared spectrum solar cell as well as other advantageous features are recited in the dependent claims.

[0037] Metamaterials (MTMs) are engineered materials which cannot be found in nature. These artificial structures exhibit extraordinary electromagnetic properties, and their anomalous behavior allows for extreme control over optical fields and enables effects such as negative refraction. The invention of the present disclosure employs the extraordinary response of MTMs to address the previously mentioned problems and inconveniences.

[0038] The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description with reference to the attached drawings showing some preferred embodiments of the invention.

[0039] A BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0040] Figure 1A shows energy absorbed by silicon technology in comparison to Sun spectral energy, and Figure 1 B is a schematic of a rectenna, and circuit model of a rectenna [3].

[0041] Figures 2 shows the results of a comprehensive survey on currently available diode technologies.

[0042] Figures 3A and 3B are schematics of exemplary ENZ MTM diodes of the present disclosure, and Figure 3C schematically shows the energy diagram of the exemplary ENZ MTM diode of the present disclosure. Figures 3D and 3E are schematics of further exemplary embodiments including a gate for applying a bias voltage.

[0043] Figures 4A to 4D are schematics of exemplary double insulator MTM diodes of the present disclosure, and Figure 4E schematically shows the energy diagram of the exemplary double insulator MTM diode of the present disclosure. Figures 4F and 4G are schematics of further exemplary embodiments including a gate for applying a bias voltage.

[0044] Figure 5 shows a simulation determined energy band diagram of the proposed MIM diode of the present disclosure, as schematically shown in Figures 3A to 3B.

[0045] Figure 6 shows a simulation determined energy band diagram of the exemplary MUG diode of the present disclosure, as schematically shown in Figures 4A to 4D.

[0046] Figures 7A to 7C show exemplary embodiments of metal terminals or electrodes of the diode of the present disclosure forming an interdigital structure. Figure 7D shows an exemplary embodiment of metal terminals or electrodes of the diode of the present disclosure forming an interdigital structure and including a coplanar waveguide (CPW) structure.

[0047] Figure 7E shows an exemplary embodiment of metal terminals or electrodes of the diode of the present disclosure forming an interdigital structure where the fingers define a modulated finger extension.

[0048] Figure 7F shows an exemplary embodiment of metal terminals or electrodes of the diode of the present disclosure forming an interdigital structure where fingers are interconnected by wire bonding to reduce resistance of the terminals.

[0049] Figure 8A to 8F schematically shows exemplary embodiments of inductors that may be connected in series with the diode junctions permitting to compensate the capacitance introduced by an interleaving or interdigital structures and keep the resistance low. Figure 8A shows a slit or slit cut inductor, Figure 8B shows a meander-line inductor, Figure 8C shows a spiral inductance. Figures 8D to 8F show other exemplary inductor structures including an inductor comprising dual spirals (Figure 8D); complementary Hilbert structure inductor(Figure 8E), and an inductor comprising fractal structures (Figure 8F) that permit to reduce a diode intrinsic resistance.

[0050] Herein, identical reference numerals are used, where possible, to designate identical elements that are common to the Figures. Also, the images are simplified for illustration purposes and may not be depicted to scale.

[0051] DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0052] The accompanying drawings constitute part of this specification, illustrate the presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain features of the invention.

[0053] Figures 3A to 3B, and 4A to 4D schematically show exemplary diodes or diode devices 1 of the present disclosure.

[0054] The diode device 1 is, for example, a rectification diode device configured to convert alternating current (AC) or alternating voltage to direct current (DC). The diode 1 can be, for example, a two- terminal electronic component or an at least two-terminal electronic component that is configured to conduct electric current in one direction or in a first direction through the device while blocking or impeding the conduction of electric current in another direction, for example, in an opposite direction or opposite direction to that of the first direction.

[0055] The diode device 1 assures, for example, a high cutoff frequency, and is, for example, a THz- cutoff frequency diode.

[0056] The diode device 1 can be, for example, a solar energy harvesting diode, or a (optical) rectenna diode or used as, for example, a solar energy harvesting diode or a (optical) rectenna diode.

[0057] Although some conventional optical dioxide materials, e.g. AI2O3, which has a relatively small dielectric constant of 0.8 at terahertz and optical frequencies, leads to small diode capacitance, it is crucial to make sure that the diode resistance is small to obtain high cutoff frequencies given that fc= 1 / (2TIRDCD).

[0058] The diode resistance increases roughly exponentially with the insulator thickness and barrier height and has an inverse linear dependence on the device area. There is almost no way to decrease the diode intrinsic resistance except by reducing the diode dimensions. However, changing the diode’s junction’s geometrical configuration could help decrease the resistor even to the quantum level

[0036] . Although the proposed geometrical approach helps reduce the intrinsic resistor, it causes an increase in the effective capacitor. Using a geometrical method in

[0037] , the concerned inventors try to introduce a high-speed diode by decreasing the resulting capacitor.

[0059] This present disclosure, however, takes a different approach and focuses on reducing the diode capacitance by decreasing the permittivity of the insulator using metamaterials MTMs. At the same time, in an embodiment, a charge carrier (electron) source material, layer or structure 9 such as a high charge carrier (electron) mobility layer, for example, a 1 D graphene layer, can be included in combination to increase the diode conversion efficiency. Other 2D materials or heterojunctions (e.g. high-mobility semiconductor heterojunctions) may be alternatively or additionally be used.

[0060] Additionally, a graphene layer can also be used as the antenna arms, or a part thereof to improve coupling efficiency between the antenna and the diode 1 , when for example the diode 1 is included in a rectenna. Figures 3A and 3B are schematics of exemplary epsilon-near-zero metamaterial (ENZ MTM) diodes of the present disclosure, that is, a diode including or loaded by an epsilon-near-zero metamaterial (ENZ MTM).

[0061] According to the below Equation 1 for diode cutoff frequency fc, decreasing the diode insulator's permittivity increases the cutoff frequency. In this formula, d is the insulator thickness, and A is the area between the capacitor junctions.

[0062] _ / c <Xl IC diode dl(Sdiode'A) (1)

[0063] The insulator according to the present disclosure is realized using epsilon-near-zero (ENZ) metamaterials or material (ENZ MTMs).

[0064] Figures 3A and 3B show embodiments of exemplary MIM / MIG diodes and the energy diagram of this structure is schematically shown in Figure 3C. Using ENZ MTMs advantageously helps to decrease the intrinsic diode capacitor / capacitance. It directly affects the diode cutoff frequency and is thus expected to achieve a high-frequency response up to mid-infrared frequencies. Moreover, the MTMs also cause the electric field to concentrate significantly at the diode terminals, improving the diode tunnelling efficiency. When the electron source material or layer 9 comprises or consists of graphene, graphene can, for example, be employed in a vertical or horizontal configuration.

[0065] The diode or diode device 1 includes, for example, at least a first metal or first metal terminal or first metal electrode or contact 3 (for example, a terminal or conductive layer comprising at least one metal), at least a second metal or second metal terminal or second metal electrode or contact 5 (for example, terminal or conductive layer comprising at least one metal); and at least one insulator, insulator material or insulator layer 7 (for example, layer comprising at least one insulator) extending between the first metal terminal 3 and the second metal terminal 5. The insulator 7 is in direct or indirect contact with the first and second metal terminals 3, 5. The insulator 7 comprises or consist solely of a dielectric insulator.

[0066] In an embodiment, the insulator 7 may comprise or consist solely of at least one epsilon-near- zero (ENZ) metamaterial or epsilon-near-zero (ENZ) material, structure or medium 7. That is, a material, structure or medium 7 having a near zero value(s) of permittivity. For example, but not limited to, a value e that is <0.1 e0where e0is the vacuum permittivity. The insulator 7 may alternatively comprise or consists solely of at least one epsilon-and-mu-near-zero (EMNZ) metamaterial or epsilon-and-mu-near-zero (EMNZ) material, structure or medium 7. That is, a material, structure or medium 7 having a near zero value(s) of permittivity and permeability. For example, but not limited to, a value e that is <0.1 e0where e0is the vacuum permittivity, and a value p that is <0.1 po where po is the vacuum permeability.

[0067] The epsilon-near-zero (ENZ) metamaterial or material 7 or the epsilon-and-mu-near-zero (EMNZ) metamaterial or material 7 is located between or extends between the first and second metal terminals 3, 5.

[0068] The terms epsilon-near-zero (ENZ) metamaterial or material 7 and epsilon-and-mu-near-zero (EMNZ) metamaterial or material 7 can be used interchangeably in below description of the diode device 1 , with the term epsilon-near-zero (ENZ) metamaterial or material 7 being used principally used in the description that follows.

[0069] In an embodiment, one or solely one insulator 7 is, for example, present in the metal-insulator- metal (MIM) diode device 1 of Figures 3A and 3B. One or solely one insulator 7 , for example, extends between the first and second metal terminals 3, 5 and the first and / or second metal terminals 3,5 are superposed on the one or solely one insulator 7.

[0070] The first metal terminal 3 and / or the second metal terminal 5 are superposed on the one epsilon- near-zero (ENZ) metamaterial or material 7. The epsilon-near-zero (ENZ) metamaterial or material 7 is, for example, in direct or indirect contact with the first and / or second metal terminals 3, 5. In the exemplary embodiments shown in Figures 3A and 3B, the epsilon-near-zero (ENZ) metamaterial or material 7 is in direct contact with both the first and second metal terminals 3, 5.

[0071] As mentioned above, the diode device 1 may include, for example, at least one electron source material, layer or structure 9 configure to provide electrons for tunneling through the insulator 7, for example, when a voltage potential difference is applied or present between the first and second terminals 3,5 or applied across the insulator 7.

[0072] The electron source material, layer or structure 9 may comprise or consist of a single-layer material or 2D material comprising or consisting of a crystalline solid, for example, having or consisting of a single-layer of atoms. For example, single-layer materials having an ‘-ene’ suffix or an ‘-ane’ suffix or an ‘-ide’ suffix.

[0073] The electron source material, layer or structure 9 may include single-layer materials or 2D materials that have a Dirac point(s) in the electronic band structure of the material. That is, the electron source material, layer or structure 9 may include at least one 2D Dirac material. For example, at least one of graphene, germanene, silicene, beryllium-based monolayers, and boron- based monolayers (for example, borophene).

[0074] Exemplary 2D Dirac materials are listed in Table 1 of page 39 of the following publication: Runyu Fan, Lei Sun, Xiaofei Shao, Yangyang Li, Mingwen Zhao, Two-dimensional Dirac materials: Tight- binding lattice models and material candidates, ChemPhysMater, Volume 2, Issue 1 , 2023, Pages 30-42, ISSN 2772-5715, https: / / doi.Org / 10.1016 / j.chphma.2022.04.009.

[0075] In a preferred embodiment, the electron source material, layer or structure 9 includes or consist of graphene as a source of electrons or charge carriers.

[0076] The diode device 1 includes, for example, at least one electron source material, layer or structure 9 comprising or consisting of a graphene layer or material or structure 9 extending between the first terminal 3 and the second metal terminal 5. The graphene layer 9 (that is, the electron source material, layer or structure for which graphene is provided in the present description and mentioned in the Figures as an exemplary embodiment) may, for example, be in contact directly or indirectly with the first terminal 3 and / or the second metal terminal 5.

[0077] In the exemplary embodiment of Figure 3A, the graphene layer 9 is in direct contact with the first metal terminal 3 and in indirect contact with the second metal terminal 5 via the insulator 7. Alternatively, the graphene layer 9 may also be in indirect contact with the first terminal 3.

[0078] In the exemplary embodiment of Figure 3B, the graphene layer 9 is in direct contact with both the first metal terminal 3 and the second metal terminal 5. Alternatively, the graphene layer 9 may also be in indirect contact with both the metal terminals 3, 5.

[0079] The graphene material or layer 9 may, for example, be arranged in the diode device 1 in a horizontal configuration as shown in Figures 3A and 3B. In the horizonal configuration, the graphene material or layer 9 comprises for example a two-dimensional graphene sheet that extends to define a planar layer or sheet superposed on and extending parallel to a planar surface PS of a support or substrate 11. The graphene material or layer 9 may, for example, be alternatively arranged in the diode device 1 in a vertical configuration. In the vertical configuration, the graphene material or layer 9 includes a plurality of vertically stacked sheets grown / provided on and / or extending substantially perpendicularly away from the plane defined by the surface PS of the support or substrate 11 , in a stacking direction Y (see Figures 3A and 3B).

[0080] The graphene layer 9 is in contact with the epsilon-near-zero (ENZ) metamaterial or material 7. The graphene layer 9 may be in direct contact, as shown in Figures 5A and 5B, but may also be in indirect contact with the epsilon-near-zero (ENZ) metamaterial or material 7. The graphene layer 9 and the epsilon-near-zero (ENZ) metamaterial or material 7 are, for example, located between the first and second metal terminals 3, 5. The graphene layer 9 is, for example, superposed on the epsilon-near-zero (ENZ) metamaterial or material 7.

[0081] The diode device 1 includes the at least one substrate or support 11 upon which the first metal terminal 3 and / or the second metal terminal 5, the graphene layer 9, and the epsilon-near-zero (ENZ) metamaterial or material 7 are provided or attached. The substrate or support 11 may, for example, comprise or consist of silicon (Si), Silicon oxide (SiCk) or quartz, provided here as nonlimiting exemplary embodiments.

[0082] In the exemplary embodiment of Figure 3A, the second metal terminal 5 is (partially) embedded, for example, embedded in the substrate or support 11 . The first metal terminal 3 is superposed on the epsilon-near-zero (ENZ) metamaterial or material 7 which is located between the first and second metal terminals 3,5. The first metal terminal 3 is, for example, in (direct or indirect) contact with the graphene layer 9. The first metal terminal 3 may also be superposed on the graphene layer 9. The graphene layer 9 and the epsilon-near-zero (ENZ) metamaterial or material 7 may, for example, be located between the first and second metal terminals 3,5. The embedded second metal terminal 5 is in (direct) contact with the epsilon-near-zero (ENZ) metamaterial or material 7. The first and second metal terminals 3,5 are, for example in an embodiment, laterally displaced with respect to each other in a lateral direction L or at different planar locations. The first and second metal terminals 3,5 are also, for example, vertically displaced (for example, in the Y- direction) with respect to each other in a height or thickness direction H of the stacked layers or materials. The epsilon-near-zero (ENZ) metamaterial or material 7 and the graphene layer 9 are, for example, superposed on the second metal terminal 5. At least a portion of the epsilon-near- zero (ENZ) metamaterial or material 7 and the graphene layer 9 are, for example, directly underlying or located directly beneath the first metal terminal 3.

[0083] In the exemplary embodiment of Figure 3A, the epsilon-near-zero (ENZ) metamaterial or material 7 and / or the graphene layer 9 extend between the first metal terminal 3 and the second metal terminal 5 in an intermediate device zone IDZ separating the first and second metal terminals 3,5.

[0084] In the exemplary embodiment of Figure 3B, both the first metal terminal 3 and the second metal terminal 5 are superposed on the epsilon-near-zero (ENZ) metamaterial or material 7 (at least a portion thereof). The first metal terminal 3 and the second metal terminal 5 may also be superposed on the graphene layer 9 (at least a portion thereof). The epsilon-near-zero (ENZ) metamaterial or material 7 contacts and / or extends between the first metal terminal 3 and the second metal terminal 5, and extends, for example, underneath the first metal terminal 3 and the second metal terminal 5. The graphene layer 9 may also contact and / or extend between the first metal terminal 3 and the second metal terminal 5 and, for example, extend (at least a portion thereof) underneath the first metal terminal 3 and the second metal terminal 5. In an embodiment, the graphene layer 9 directly contacts the first metal terminal 3 and / or the second metal terminal 5, and directly contacts the epsilon-near-zero (ENZ) metamaterial or material 7.

[0085] A portion of the electron source material, layer or structure 9 may, for example, comprise or define a metal terminal-free section located between the first and second metal terminals 3,5.

[0086] As schematically illustrated in Figure 3C, in an advantageous embodiment, a work function <pi of a metal of the first metal terminal 3 is preferably greater than a work function q>2 of a metal of the second metal terminal 5. The first metal terminal 3 may comprise or consist of at least one first metal, and the second metal terminal 5 may comprise or consist of at least one second metal, the first and second metals being different metals. The first metal terminal 3 may, for example, comprise or consist solely of gold Au, and / or the second metal terminal 5 may, for example, comprise or consist solely of titanium Ti.

[0087] The thickness of the metal terminals 3, 5 can, for example, be between 10 and 300nm, for example 200nm. The epsilon-near-zero (ENZ) metamaterial or material 7 is configured to provide near-zero permittivity in the infrared-visible wavelength / frequency ranges. The thickness of the epsilon- near-zero (ENZ) metamaterial or material 7 is for example, between 1 nm and 50nm, for example 5nm.The epsilon-near-zero (ENZ) metamaterial or material 7 is configured to provide broadband operation, for example, in the visible-infra red spectrum or wavelength / frequency range.

[0088] The permittivity of the dielectric insulator 7 is near zero as defined by at least one epsilon-near- zero (ENZ) metamaterial or material to provide a diode device 1 having a reduced intrinsic diode capacitance.

[0089] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may be implemented or realized in various different and / or known manners.

[0090] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may, in an embodiment, comprise a stacked or multilayer structure that provides, for example, a broadband ENZ metamaterial. Figure 3F schematically shows such an exemplary stacked or multilayer structure. The stacked or multilayer structure includes, for example, a metal layer 25A comprising or consisting at least one epsilon negative material (for example, a metal such as gold, silver or aluminium of thickness for example between 10nm and 25nm), a double positive material such as a dielectric layer 25B comprising or consisting at least one dielectric material (for example, an oxide dielectric material such as aluminium oxide of thickness for example between 10nm and 50nm), optionally at least one epsilon negative material such as a metal layer 25C comprising or consisting at least one metal (for example, gold, silver or aluminium (for example, different to that of metal layer 25A) of thickness for example between 10nm and 25nm), and a graphene layer or sheet 25D. The graphene layer or sheet 25D may, for example, also form the electron source material, layer or structure 9 of the device 1.

[0091] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may be implemented or realized using a composite material such as thin indium tin oxide (ITO) which exhibits an ENZ effect in the optical regime.

[0092] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may, for example, be implemented or realized in any one of the manners disclosed in the article by Liberal, I., Engheta, N. entitled ‘Near-zero refractive index photonics’ published in Nature Photon 11 , 149-158 (2017). https: / / doi.org / 10.1038 / nphoton.2017.13, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes. The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may comprise in particular any one of the embodiments disclosed in relation to Figures 4b(i) to 4b(iii) of this Liberal et al article and described in detail in the associated referenced documents the disclosure of each of which is hereby incorporated herein by reference in its entirety for all purposes.

[0093] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may, for example, comprise a waveguide operating at its cutoff frequency (see Figure 4b(i) of the Liberal et al article) or a periodic wire structures (see Figure 4b(ii) of the Liberal et al article).

[0094] The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may, for example, comprise a periodic dielectric structures with alternating positive and negative permittivity (see Figure 4b(iii) of the Liberal et al article). For instance, an Ag / SiN multilayered structure as disclosed in the publication by Maas, R., Parsons, J., Engheta, N., & Polman, A. (2013), entitled ‘Experimental realization of an epsilon-near-zero metamaterial at visible wavelengths’, published in Nature Photonics, 7(11 ), 907-912, https: / / doi.org / 10.1038 / nphoton.2013.256.

[0095] In another embodiment, the epsilon-near-zero (ENZ) metamaterial or material 7 can be realized, for example, as described in

[0039] . The epsilon-near-zero (ENZ) metamaterial, structure or medium 7 may, for example, comprise the structure described in US Patent 11 ,502,383, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes. The epsilon-near- zero (ENZ) metamaterial, structure or medium 7 or epsilon-and-mu-near-zero (EMNZ) material, structure or medium 7 includes at least one waveguide, a length I of the waveguide satisfying a length condition according to l<0.1A, where A is an operating wavelength of the EMNZ metamaterial 7. An exemplary waveguide may include one of a rectangular waveguide and a parallel-plate waveguide. The EMNZ metamaterial 7 may further include a magneto-dielectric material, for example, deposited on a lower wall of the waveguide. The waveguide may further include an impedance surface. An exemplary impedance surface may be placed on the magnetodielectric material. In an exemplary embodiment, the impedance surface may include a tunable impedance surface. An exemplary tunable impedance surface may include a tunable conductivity. An exemplary tunable impedance surface may include a monolayer graphene. In an exemplary embodiment, a dielectric spacer may be provided or coated on the monolayer graphene and attached to an upper wall of the waveguide. In an exemplary embodiment, a thickness h of the dielectric spacer may satisfy a thickness condition according to h<A4, where A is an operating wavelength of the EMNZ metamaterial 7. A permittivity of the dielectric spacer may be equal or substantially equal to a permittivity e of the magneto-dielectric material. In an exemplary embodiment, a permeability pof the dielectric spacer may be equal or substantially to a permeability p of the magneto-dielectric material. An exemplary monolayer graphene may be attached to a left sidewall of the rectangular waveguide and a right sidewall of the rectangular waveguide. A cutoff frequency fcis for example configured to be adjusted by adjusting a chemical potential pcof the monolayer graphene. The cutoff frequency fcmay be configured to be adjusted based on a distance between the upper wall and a lower wall of the waveguide and based on an effective permittivity of the magneto-dielectric material and the monolayer graphene. The cutoff frequency fcis defined by the equation as set out in the claims of US Patent 11 ,502,383.

[0096] This structure 7 provides broadband ENZ or EMNZ behavior. This structure 7 features a waveguide loaded with an impedance boundary condition, utilizing a (low-loss) 2D material of which one example is provided in this patent is graphene used as an impedance boundary condition, although it should be noted that other materials exhibiting such behavior may alternatively be used.

[0097] As previously mentioned, the ENZ or EMNZ metamaterial, structure or medium 7 is located between or sandwiched between the first and second metal terminals 3,5 and is in contact and electrically connected to the first and second metal terminals 3,5 for a voltage potential difference to be applied across or to the ENZ or EMNZ metamaterial, structure or medium 7 to allow or restrict current flow through the device 1 depending on the polarity applied to the first and second metal terminals 3,5.

[0098] The device 1 may, for example, include at least one ENZ or EMNZ metamaterial, structure or medium 7, or a plurality thereof.

[0099] The epsilon-near-zero (ENZ) metamaterial or material 7 can be realized by artificial material or any other kind of materials that can, for example, provide a broadband near-zero permittivity in the infrared / visible spectrum.

[0100] Figure 5 shows a simulation determined energy band diagram of the exemplary MIM diode 1 shown in Figures 3A and 3B. The metals 3, 5 are for example Au and Ti, while the insulator 7 is the ENZ metamaterial 7. The thickness of the insulator 7 was set to be 5nm for the simulation results shown in Figure 5. To provide near-zero permittivity, the insulator 7 is realized by ENZ metamaterials. The ENZ metamaterial 7 is realized as described in

[0039] . The diode structure is simulated using SILVACO (TCAD and ATLAS), and the energy diagram of the structure is presented in Figure 5. According to the simulation results as presented in this figure, the diode structure provides an asymmetrical response. The insulator's near-zero permittivity helps increase the electric field strength, leading to a significant enhancement in diode capacitor / capacitance. According to Equation (1), the cut-off frequency is about 1500 THz. The 1D graphene layer 9 provides an infinite source of electrons during the tunnelling process thus improving the diode efficiency.

[0101] According to another embodiment, the diode 1 includes at least one gate or gate terminal or electrode 17. The gate terminal 17 is provided on and in contact, for example directly or indirectly, with the (for example, a portion thereof) the electron source material, layer or structure 9. The gate terminal 17 may be provided on and in contact (for example, indirectly) with the ENZ metamaterial 7. The gate 17 is for example located (at least partially) between the first terminal 3 and the second terminal 5. This permits a bias voltage to be applied to the electron source material, layer or structure 9 and the gate to be used for reconfigurability of the device 1 , or for operation of the device 1 as a transistor. Figures 3D and 3E are schematics of the device 1 including the gate 17 for applying a bias voltage.

[0102] According to an embodiment, the first terminal 3 and the second terminal 5 interpenetrate or interleave. The interpenetrating or interleaving first and second terminals 3, 5 are separated by a separation gap GP. The separation gap GP preferably is of (substantially) constant value or distance (see, for example, Figures 7A to 7F).

[0103] The first terminal 3 and the second terminal 5 form an interpenetrating or interleaving structure 27.

[0104] The first terminal 3 may, for example, include or define at least one recess 33 and the second terminal 5 may, for example, include or define at least one protrusion 29B extending into the at least one recess 33. The first terminal 3 may, for example, include or define a plurality of recesses 33 and the second terminal 5 may, for example, include or define a plurality of protrusions 29B extending into the recesses 33.

[0105] Alternatively, the second terminal 5 may, for example, include or define at least one recess 33 and the first terminal 3 may, for example, include or define at least one protrusion 29A extending into the at least one recess 33. The second terminal 5 may, for example, include or define a plurality of recesses 33 and the first terminal 3 may, for example, include or define a plurality of protrusions 29A extending into the recesses 33.

[0106] The protrusion 29A of the first terminal 3 is, for example, separated from the protrusion of the second terminal 5 by a separation gap GP.

[0107] Exemplary illustrated embodiments are shown in Figures 7A to 7F.

[0108] This permits to reduce the resistance of the device 1 to enhance the device cutoff frequency.

[0109] In an exemplary embodiment, the first terminal 3 and the second terminal 5 are, for example, each structured to include or define a plurality of metallic protrusions or fingers 29A, 29B. The fingers 29A of the first terminal 3 extend away from a first support portion 31A of the first metal terminal 3 towards a second support portion 31 B of the second terminal 5. The fingers 29B of the second terminal 5 extend away from the second support portion 31 B towards the first support portion 31 A of the first terminal 3.

[0110] The metallic fingers or protrusions 29A, 29B may, for example, be elongated. The metallic fingers or protrusions 29A, 29B may, for example, extend (substantially) linearly, or extend in a curved manner.

[0111] The interdigital or interleaving structure 27 is formed by the metallic protrusions or fingers 29A, 29B being arranged to form a plurality of interleaving metallic protrusions or fingers 29A, 29B, the interleaving metallic protrusions or fingers 29A, 29B being separated by the at least one recess 33 where the metal material is removed or absent.

[0112] The recess 33 extends in a winding or meandering manner to define a plurality of interleaving metallic extensions or fingers 29A, 29B separated by the recess 33. The recess 33 may, for example, extend (substantially) linearly in a winding or meandering manner, or extend in a curved manner and in a winding or meandering manner.

[0113] The first metallic fingers 29A of the first terminal 3 are located adjacent to the at least one second metallic finger 29B of the second terminal 5 and separated by the recess 33. Different exemplary embodiments of the interdigital or interleaving structure 27 are illustrated in Figures 7A to 7D.

[0114] The device 1 may, in an embodiment, including a coplanar waveguide (CPW) structure 35 surrounding or enclosing the interdigital or interleaving structure 27. Figure 7D shows an exemplary embodiment.

[0115] According to another embodiment, the fingers 29A of the first terminal 3 are electrically interconnected, for example, by wire bonding. Similarly, the fingers 29B of the second terminal are electrically interconnected, for example, by wire bonding. This permits to reduce the resistance of the terminals.

[0116] In an embodiment, the metallic fingers 29A, 29B or each finger 29A, 29B may, for example, define or include a rim 37 that extends in an oscillating or undulating manner. For example, extending to form a sawtooth comprising a plurality of teeth 39 profile as shown in the exemplary embodiment of Figure 7E.

[0117] In another embodiment, the device 1 may include at least one inductor 39 connected in series with the diode 1 or diode junction. This permits to compensate the capacitance introduced by the interdigital or interleaving structure 27 and to keep resistance low. Alternatively, the at least one inductor 39 may be included on a separate device and connected in series with the diode or device 1. The inductor 39 includes at least one coil or elongated member 41 extending inside and / or on a host or supporting layer or substrate (for example, dielectric). The coil or elongated member comprises at least one metal, for example, gold.

[0118] Figure 8A to 8F schematically shows exemplary embodiments of inductors 39. Figure 8A shows a slit or slit cut inductor, Figure 8B shows a meander-line inductor, and Figure 8C shows a spiral inductance.

[0119] Figures 8D to 8F show other exemplary inductor structures including an inductor comprising dual spirals (Figure 8D); a complementary Hilbert structure or Hilbert fractal inductor (Figure 8E), and an inductor comprising fractal structures (Figure 8F) that permit to reduce a diode intrinsic resistance. Figures 4A to 4D are schematics of further exemplary embodiments of the device or diode 1 of the present disclosure in which the diodes are loaded by at least one epsilon-negative (ENG) metamaterial or material.

[0120] Using epsilon-near-zero (ENZ) metamaterial ENZ MTM, although it helps to decrease the diode insulator permittivity, it can increase the electric field intensity and the guided wavelength to approach infinity, which reduces the electron tunnelling probability.

[0121] To avoid this unwanted quantum consequence, the exemplary embodiment of Figures 4A to 4D replace the insulator 7, which has near-zero permittivity, with a double insulator structure 15. In this diode structure, two dielectric materials are employed with different or opposite permittivity signs but the same absolute value (or substantially the same absolute value). By using two materials with opposite signs, the electric field distribution can be modified to minimize the likelihood of electron tunnelling being adversely affected. At the same time, it is possible to maintain a low diode insulator permittivity which leads to improving the diode operating frequency. Moreover, the exemplary 1D graphene layer 9 enhances the diode conversion efficiency like a single insulator structure.

[0122] The exemplary embodiments of Figures 4A and 4B are identical to those of Figures 3A and 3B as described above, except that the insulator 7 comprises or consists solely of a first insulator or insulator layer 7A, the first insulator 7A comprising or consisting solely of at least one epsilonnegative (ENG) metamaterial or material.

[0123] The at least one epsilon-negative (ENG) metamaterial or material or material 7A is, for example, configured to provide a negative capacitance to provide a reduced effective intrinsic capacitance value of the diode device 1 .

[0124] Preferably, the insulator 7 further includes a second insulator or insulator layer 7B, and the first insulator 7A and the second insulator 7B define or form a double insulator structure 15. The first insulator 7A is a different insulator to that of the second insulator 7B.

[0125] The insulator 7 may thus comprise or consist only of the double insulator structure 15. The first insulator 7A and the second insulator 7B may. For example, extend parallel to one another while being superposed on each other as, for example, shown schematically in Figures 6A and 6B. The first insulator 7A may comprise or consists solely of the at least one epsilon-negative (ENG) metamaterial or material.

[0126] The double insulator structure 15 extends between the first and second metal terminals 3, 5, and the first and / or second metal terminals 3,5 are superposed on the double insulator structure 15.

[0127] The graphene layer 9 is superposed on the double insulator structure 15. The graphene layer 9 is, for example, superposed on the first insulator 7A and / or the second insulator 7B.

[0128] In the exemplary embodiments of Figures 4A and 4B that show a series configuration embodiment, the second insulator 7B is located or arranged in the diode device 1 in an identical manner to that of the insulator 7 of the previously described diode device 1 , described in relation to the diode device of the previous embodiments of which exemplary embodiments are schematically shown in Figure 3A and 3B. The second insulator 7B is superposed on the first insulator 7A, comprising or consisting solely of at least one epsilon-negative (ENG) metamaterial or material, is located, and in contact with (directly or indirectly) the first insulator 7A.

[0129] The second insulator 7B is superposed on the first insulator 7A to form a series configuration between the first metal terminal 3 and the second metal terminal 5.

[0130] The first insulator 7A is superposed on the substrate or support 11 and in contact therewith. The first insulator 7A is, for example, located between the substrate or support 11 and the second insulator 7B.

[0131] However, in an alternative embodiment, the positions of first insulator 7A and the second insulators 7B shown in Figures 4A to 4D may be inversed.

[0132] In the exemplary embodiment of Figure 4A, the double insulator structure 15 and / or the electron source material, layer or structure 9 that is the graphene layer 9 in the illustrated embodiment extend between the first metal terminal 3 and the second metal terminal 5 in an intermediate device zone IDZ separating the first and second metal terminals 3,5.

[0133] In the exemplary embodiment of Figure 4B, both the first metal terminal 3 and the second metal terminal 5 are superposed on the double insulator structure 15. The first metal terminal 3 and the second metal terminal 5 may also be superposed on the graphene layer 9. The double insulator structure 15 extends between the first metal terminal 3 and the second metal terminal 5 and underneath the first metal terminal 3 and the second metal terminal 5. The graphene layer 9 may also extend between the first metal terminal 3 and the second metal terminal 5 and underneath the first metal terminal 3 and the second metal terminal 5.

[0134] The exemplary embodiments of Figures 4C and 4D show shunt configuration embodiments in which the first insulator 7A contacts the second insulator 7B to form at least one lateral insulator interface junction 19 and to form a shunt configuration between the first metal terminal 3 and the second metal terminal 5.

[0135] The double insulator structure 15 is defined by the first insulator 7A arranged side-by-side with the second insulator 7B, or arranged in lateral contact the second insulator 7B. The double insulator structure 15 is defined or comprises one layer in which a first layer portion is defined by the first insulator 7A and a second layer portion is defined by the second insulator 7B that, at the lateral insulator interface junction 19, contacts and extends from the first insulator 7A.

[0136] The first layer portion comprising the first insulator 7A may, for example, be located underneath or above one of the metal terminals (for example, the second metal terminal 5), and the second layer portion comprising the second insulator 7B may, for example, be located underneath or above one of the other metal terminal (for example, the first metal terminal 3).

[0137] The electron source material, layer or structure 9 that is the graphene layer 9 in the illustrated embodiment extends across and is in contact with the double insulator structure 15 and the lateral insulator interface junction 19. The lateral insulator interface junction 19 extends, for example, from the graphene layer 9 in the height or thickness direction H towards the substrate 11 .

[0138] In the exemplary embodiments of Figures 4A to 4D, the first insulator 7A has a permittivity value in the visible and infrared wavelength / frequency ranges of the same or substantially the same absolute value as that of the second insulator 7A and of opposite sign to that of the second insulator 7A, to modify an electric field distribution and promote electron tunnelling in the diode device 1. The epsilon-negative (ENG) metamaterial or material preferably has a negative permittivity value in visible and infrared wavelength / frequency ranges.

[0139] The epsilon-negative (ENG) metamaterial or material 7A is preferably configured to provide a broadband negative permittivity in infrared and / or visible wavelength / frequency ranges. The epsilon-negative (ENG) metamaterial or material 7A is configured to provide a negative capacitance in a series or shunt configuration with the intrinsic capacitance to provide a reduced effective intrinsic capacitance value of the diode device 1 .

[0140] The first insulator 7A has an electron affinity Ei different to an electron affinity E2of the second insulator 7B.

[0141] As schematically illustrated in Figure 4E, a work function <pi of a metal of the first metal terminal 3 is preferably greater than a work function <p2 of a metal of the second metal terminal 5. The first metal terminal 3 may comprise or consist of at least one first metal, and the second metal terminal 5 may comprise or consist of at least one second metal, the first and second metals being different metals. The first metal terminal 3 comprises or consists solely of, for example, Niobium (Nb), and / or the second metal terminal 5 comprises or consists solely of, for example, Niobium nitride (NbN).

[0142] The epsilon-negative (ENG) metamaterial or material 7A comprises or consists of, for example, a titanium hydride (TiHx), for example, TiH2.

[0143] The epsilon-negative (ENG) metamaterial or material 7A can, for example, be realized by artificial structures or any other kind of materials that can provide broadband desired negative permittivity in the infrared / visible spectrum.

[0144] The epsilon-negative (ENG) metamaterial or material 7A may be realized in different ways. For example, as a multilayer structure comprising for example alternative metal and dielectric layers such as aluminium and SiO2layers, as for example described in the article by Bang, S., So, S. & Rho, J., entilted “Realization of broadband negative refraction in visible range using vertically stacked hyperbolic metamaterials”, published in Sci Rep 9, 14093 (2019). https: / / doi.org / 10.1038 / s41598-019-50434-3, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

[0145] The epsilon-negative (ENG) metamaterial or material 7A may, for example, be realized using periodic structures, comprising double silver strips and AI2O3, as described in the article by Shalaev, V., Kildishev, A., Klar, T., Popov, A., & Drachev, V, entitled ‘Optical Negative-Index Metamaterials: from low to no-loss and from linear to nonlinear optics’, published in LEOS 2006- 19th Annual Meeting of the IEEE Lasers and Electro-Optics Society, Montreal, QC, Canada, 2006, pp. 246-247, doi: 10.1109 / LEOS.2006.279021 , the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

[0146] The epsilon-negative (ENG) metamaterial or material 7A may, for example, be realized by means of alloys as described in “Dynamic optical properties of metal hydrides” by Palm K.J. et al and published by ACS Photonics, 5(11 ), 4677- 4686, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes, and described in the article by Palm, K. J., et al., (2019) entitled ‘In situ optical and stress characterization of alloyed PdxAui_xhydrides’, published in ACS Applied Materials & Interfaces, 11 (48), 45057-45067 the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

[0147] The second insulator 7B may, for example, comprise or consist of Aluminium oxynitride.

[0148] The ENG materials 7A are employed to realize a negative capacitor. In parallel with the intrinsic diode capacitor / capacitance, the negative capacitor diminishes the total capacitor and causes the cutoff frequency to increase significantly, as can be understood from equations 2a and 2b below. Additionally, the use of, for example, graphene 9 can enhance the efficiency of the diode 1 . Furthermore, the double insulator structure 15 can naturally increase the non-linearity of the diode 1. These features can lead to improved performance of the diode 1 in various applications.

[0149] Vediode =VeI +VeENG ~0 (Series Configuration) (2a) ediode = l+ eENG~ (Shunt Configuration) (2b)

[0150] The epsilon-negative (ENG) metamaterial(s) or material(s) 7A is used to realize a negative capacitance (in the series / shunt configurations) that, taking into account the intrinsic diode capacitor / capacitance, produces an effective intrinsic capacitor / capacitance of the diode 1 that is minimized or adjusted to zero (einsulator=~£ENG )■

[0151] Figure 6 shows results of a simulation determining the energy band diagram of the MUG diode schematically shown in Figures 4A to 4D. The metals 3,5 are assumed to be Nb and NbN in the simulation, while the insulators 7B, 7A are AIN-AI2O3(Aluminium oxynitride, ALON) and TiH2 respectively- The thickness of each of the insulators 7A, 7B is considered to be equal in the simulation and to be, for example, 2 nm for each insulator 7A, 7B. The thickness of the metal terminals 3, 5 can, for example, be between 10 and 300nm, for example 200nm.

[0152] The first insulator 7A and / or the second insulator 7B may, for example, comprise or consist solely of a dielectric insulator.

[0153] The permittivity of AIN-AI2O3is about 3, while the permittivity of TiH2equals 0.1 to about - 3.5 (with the value of -3 from 1000-2500 nm) through the entire optical frequency band (200-2500 nm). The simulation was also carried out using SILVACO, and the energy diagram of the diode structure is presented in Figure 6.

[0154] According to the results of this Figure 6, the diode structure is expected to have an asymmetrical response, while the double insulator 15 assures improved nonlinearity as required for example in solar harvesting applications. The negative permittivity of the additional insulator 7B helps to decrease the diode effective capacitor / capacitance and increase the cutoff frequency up to visible range and Infrared frequencies.

[0155] According to another embodiment, the diode 1 includes at least one gate or gate terminal or electrode 17. The gate terminal 17 is provided on and in contact, for example directly or indirectly, with the (for example, a portion thereof) the electron source material, layer or structure 9. The gate terminal 17 may be provided on and in contact (for example, indirectly) with the double insulator structure 15. The gate 17 is for example located (at least partially) between the first terminal 3 and the second terminal 5. This permits a bias voltage to be applied to the electron source material, layer or structure 9 and the gate to be used for reconfigurability of the device 1 , or for operation of the device 1 as a transistor. Figures 4F and 4G are schematics of the device 1 including the gate 17 for applying a bias voltage.

[0156] According to another embodiment, and as described previously with respect to the embodiments of Figures 3A and 3B and in relation to Figure 7A to 7F, the first terminal 3 and the second terminal 5 may form the interdigital or interleaving structure 27. This permits to reduce the resistance of the device 1 to enhance the device cutoff frequency. In another embodiment, the device 1 may include the at least one inductor 39 connected in series with the diode 1 or diode junction. This permits to compensate the capacitance introduced by the interdigital or interleaving structure 27 and to keep resistance low. Alternatively, the at least one inductor 39 may be included on a separate device and connected in series with the diode or device 1. The inductor 39 includes at least one coil or elongated member 41 extending inside and / or on a host or supporting layer or substrate (for example, dielectric). The coil or elongated member comprises at least one metal, for example, gold.

[0157] Figure 8A to 8F schematically shows exemplary embodiments of inductors 39. Figure 8A shows a slit or slit cut inductor, Figure 8B shows a meander-line inductor, and Figure 8C shows a spiral inductance.

[0158] Figures 8D to 8F show other exemplary inductor structures including an inductor comprising dual spirals (Figure 8D); a complementary Hilbert structure or Hilbert fractal inductor (Figure 8E), and an inductor comprising fractal structures (Figure 8F) that permit to reduce a diode intrinsic resistance.

[0159] The diode device 1 may, for example, be a rectenna diode.

[0160] A further aspect of the present disclosure concerns a rectenna 21 , for, for example, harvesting solar energy (see, for example, Figure 1 B), for example, in both the visible spectrum and infrared spectrum. The rectenna 21 includes at least one of a plurality of device diodes 1.

[0161] The present disclosure concerns a solar / light energy harvesting method comprising providing the diode 1 as described herein, providing at least one antenna, and assembling or coupling the at least one antenna to the diode 1 to form a rectenna (an antenna coupled to a rectifying diode, see for example Figure 1 B). Solar / light energy is provided to the antenna of the rectenna to generate a rectified signal provided by the diode 1 . The rectified signal can then be provided to at least one further component / element such as an electronic / electrical component, for example, a DC filter. The rectified signal can then be provided for powering a device or for storage to a storage device.

[0162] The rectenna 21 is, for example, an optical rectenna or a visible-infrared frequency spectrum rectenna. The visible-infrared rectenna 21 includes, for example, at least one antenna or nano-antenna 23 and at least one diode device 1. The antenna or nano-antenna 23 may, for example, be a dipole antenna structure, or a spiral antenna structure, or a bowtie antenna structure.

[0163] The diode device 1 is coupled to the nano-antenna 23 and configured to rectify, to direct current (DC), an alternating current or voltage provided by the nano-antenna 23 during visible and / or infrared electromagnetic radiation capture by the nano-antenna 23.

[0164] The nano-antenna 23 includes at least arm 25A, 25B or a first arm 25A and a second arm 25. The first arm 25A and / or a second arm 25B may, for example, comprise or consist solely of graphene. This permits to improve coupling efficiency between the nano-antenna 23 and the diode device 1 .

[0165] Yet another aspect of the present disclosure concerns a solar cell or a visible-infrared spectrum solar cell. The solar cell includes at least one or a plurality of diode devices 1 ; and / or the rectenna 21.

[0166] While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments, and equivalents thereof, are possible without departing from the sphere and scope of the invention. The features of any one of the described embodiments may be included in any other of the described embodiments. The methods steps are not necessary carried out in the exact order presented above and can be carried out in a different order. Accordingly, it is intended that the invention not be limited to the described embodiments, and be given the broadest reasonable interpretation in accordance with the language of the appended claims

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[0205] Each one of the above references being fully incorporated herein by reference, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

Claims

1. CLAIMS1. Diode device (1 ) including:- a first metal terminal (3) and a second metal terminal (5);- at least one insulator (7) extending between the first and second metal terminals (3,5) and in contact with the first and second metal terminals (3,5); wherein the at least one insulator (7) comprises or consists solely of at least one epsilon-near- zero (ENZ) metamaterial or material (7), a permittivity of the at least one insulator (7) being defined by the at least one epsilon-near-zero (ENZ) metamaterial or material (7) to provide an intrinsic diode capacitance permitting an operation frequency in a visible or infrared frequency spectrum, or comprises or consists solely of at least one epsilon-negative (ENG) metamaterial or material (7A) forming, with a second insulator material (7B), at least one double insulator structure (15), wherein the at least one epsilon-negative (ENG) metamaterial or material (7A) is configured to provide a negative capacitance and an effective intrinsic capacitance value of the at least one double insulator structure (15) permitting an operation frequency in a visible or infrared frequency spectrum, and wherein the diode device (1) includes at least one electron source layer (9) extending between the first and second metal terminals (3,5) and in contact with the at least one epsilon-near-zero (ENZ) metamaterial or material (7) or the at least one epsilon-negative (ENG) metamaterial or material (7A).

2. Diode device (1 ) according to claim 1 , wherein the at least one electron source layer (9) comprises or consists of at least one graphene layer (9).

3. Diode device (1 ) according to any one of the previous claims, wherein the first terminal (3) and the second terminal (5) interpenetrate.

4. Diode device (1) according to the previous claim, wherein the interpenetrating or interleaving first and second terminals (3, 5) are separated by a separation gap (GP) of a substantially constant value or distance.

5. Diode device (1 ) according to the previous claim 3 or 4, wherein the first terminal (3) and the second terminal (5) form an interpenetrating or interleaving structure (27).

6. Diode device (1 ) according to the previous claim 3 to 5, wherein the first terminal (3) includes at least one recess (33) and the second terminal (5) includes at least one protrusion (29B) extending into the at least one recess (33), or the first terminal (3) includes a plurality of recesses (33) and the second terminal (5) includes a plurality of protrusions (29B) extending into the recesses (33).

7. Diode device (1 ) according to the previous claim 3 to 5, wherein the second terminal (5) includes at least one recess (33) and the first terminal (3) includes at least one protrusion (29A) extending into the at least one recess (33), or the second terminal (5) includes a plurality of recesses (33) and the first terminal (3) includes a plurality of protrusions (29A) extending into the recesses (33).

8. Diode device (1 ) according to the previous claim 3 to 7, wherein the first terminal (3) and the second terminal (5) are each structured to include a plurality of metallic protrusions (29A, 29B), the protrusions (29A) of the first terminal (3) extending away from a first support portion (31 A) of the first metal terminal (3) towards a second support portion (31 B) of the second terminal (5), and the fingers (29B) of the second terminal (5) extending away from the second support portion (31 B) of the second terminal (5) towards the first support portion (31 A) of the first terminal (3).

9. Diode device (1 ) according to any one of the previous claims, including at least one gate terminal (17).

10. Diode device (1 ) according to the previous claim, wherein the gate terminal (17) is provided on and in contact with the the electron source layer (9) for a bias voltage to be applied to the electron source layer (9).

11. Diode device (1 ) according to the previous claim 9 or 10, wherein the gate terminal (17) is located between the first terminal (3) and the second terminal (5).

12. Diode device (1 ) according to any one of the previous claims, including at least one inductor (39) connected in series with the first terminal (3) and the second terminal (5).

13. Diode device (1 ) according to any one of the previous claims 1 , wherein the (i) at least one epsilon-near-zero (ENZ) metamaterial or material (7) or (ii) the at least one epsilon-negative (ENG) metamaterial or material (7A) is located between the first and second metal terminals (3,5).

14. Diode device (1 ) according to any one of the previous claims, wherein the first metal terminal (3) and the second metal terminal (5) are superposed on the at least one epsilon-near-zero (ENZ) metamaterial or material (7), or on the at least one epsilon-negative (ENG) metamaterial or material (7A).

15. Diode device (1 ) according to claim 1 , wherein (i) the at least one electron source layer (9) and (ii) the at least one epsilon-near-zero (ENZ) metamaterial or material (7) or the at least one epsilon-negative (ENG) metamaterial or material (7A) are located between the first and second metal terminals (3, 5).

16. Diode device (1 ) according to any one of the previous claims, wherein the at least one electron source layer (9) is superposed on the at least one epsilon-near-zero (ENZ) metamaterial or material (7) or on the at least one epsilon-negative (ENG) metamaterial or material (7A).

17. Diode device (1) according to any one of the previous claims, including at least one substrate or support (11 ) upon which the first and / or second metal terminals (3,5), the at least one electron source layer (9), and (i) the at least one epsilon-near-zero (ENZ) metamaterial or material (7) or (ii) the at least one epsilon-negative (ENG) metamaterial or material (7A) are provided.

18. Diode device (1) according to any one of the previous claims 2 to 17, wherein the at least one graphene layer (9) extends in a horizontal or vertical configuration between the first and second metal terminals (3,5).

19. Diode device (1) according to any one of the previous claims, wherein a work function <pi of a metal of the first metal terminal (3) is greater than a work function q>2 of a metal of the second metal terminal (5).

20. Diode device (1 ) according to any one of the previous claims, wherein the first metal terminal comprises or consists of a different metal to that of the second metal terminal (5).

21. Diode device (1 ) according to any one of the previous claims, comprising one or solely one insulator (7) extending between the first and second metal terminals (3,5) and upon which the first and / or second metal terminal (3,5) are superposed, the one or solely one insulator (7) comprising or consisting solely of at least one epsilon-near-zero (ENZ) metamaterial or material (7).

22. Diode device (1 ) according to any one of the previous claims, wherein the at least one epsilon- near-zero (ENZ) metamaterial or material (7) is configured to provide a broadband near-zero permittivity in infrared and / or visible frequency ranges.

23. Diode device (1 ) according to any one of the previous claims, wherein the diode device (1 ) is a metal-insulator-metal (MIM) diode device.

24. Diode device (1 ) according to any one of the previous claims, wherein the at least one insulator (7) comprises a dielectric insulator.

25. Diode device (1 ) according to any one of the previous claims, wherein the first metal terminal (3) comprises or consists solely of titanium (Ti), and / or the second metal terminal (5) comprises or consists solely of gold (Au).

26. Diode device (1 ) according to any one of the previous claims, wherein the permittivity of the insulator (7) is near zero as defined by at least one epsilon-near-zero (ENZ) metamaterial or material (7) to provide an intrinsic diode capacitance allowing a cutoff frequency of the diode device (1) to be in the visible or infrared frequency spectrum.

27. Diode device (1) according to any one of the previous claims 1 to 20, wherein the at least one epsilon-negative (ENG) metamaterial or material (7A) is configured to provide a negative capacitance to provide a reduced effective intrinsic capacitance value of the diode device (1).

28. Diode device (1 ) according to any one of the previous claims 1 to 20, or 27, wherein the double insulator structure (15) comprises or consists solely of a first insulator (7A) and a second insulator (7B), the first insulator (7A) comprising or consisting solely of the at least one the at least one epsilon-negative (ENG) metamaterial or material (7A), the first insulator (7A) being different to the second insulator (7B).

29. Diode device (1 ) according to the previous claim, wherein the double insulator structure (15) extends between the first and second metal terminals (3,5), and the first and / or second metal terminal (3,5) are superposed on the double insulator structure (15).

30. Diode device (1) according to the previous claim 28 or 29, wherein the first insulator (7A) has a permittivity value in the visible and infrared frequency ranges of the same or substantially the same absolute value as that of the second insulator (7B) and of opposite sign to that of the second insulator (7B).

31. Diode device (1 ) according to the previous claim, wherein the at least one epsilon-negative (ENG) metamaterial or material (7A) has a negative permittivity value in the visible and infrared frequency ranges.

32. Diode device (1 ) according to any one of the previous claims 28 to 31 , wherein the first insulator (7A) has an electron affinity Ei different to an electron affinity E2of the second insulator (7B).

33. Diode device (1 ) according to any one of the previous claims 27 to 32, wherein at least one graphene layer (9) is superposed on the first insulator (7A) and / or the second insulator (7B).

34. Diode device (1 ) according to any one of the previous claims 1 to 20, or 27 to 33 wherein the at least one epsilon-negative (ENG) metamaterial or material (7A) is configured to provide a negative capacitance in a series or shunt configuration with an intrinsic capacitance to provide a an effective intrinsic capacitance value of the diode device (1 ) allowing a diode cutoff frequency in the infrared and / or visible frequency spectrum.

35. Diode device (1 ) according to any one of the previous claims 28 to 34, wherein the second insulator (7B) is superposed on the first insulator (7A) to form a series configuration between the first metal terminal (3) and the second metal terminal (5); or the first insulator (7A) contacts the second insulator (7B) to form at least one lateral insulator interface junction (19) to form a shunt configuration between the first metal terminal (3) and the second metal terminal (5).

36. Diode device (1 ) according to any one of the previous claims, wherein the at least one epsilonnegative (ENG) metamaterial or material (7A) is configured to provide a broadband negative permittivity in infrared and / or visible frequency ranges.

37. Diode device (1 ) according to any one of the previous claims 1 to 20, or 28 to 36 wherein the first metal terminal (3) comprises or consists solely of Niobium (Nb), and / or the second metal terminal (5) comprises or consists solely of Niobium nitride (NbN).

38. Diode device (1 ) according to any one of the previous claims 1 to 20, or 28 to 37, wherein the at least one epsilon-negative (ENG) material (7A) comprises or consists of a titanium hydride (TiHx), and / or the second insulator (7B) comprises or consists of Aluminium oxynitride.

39. Diode device (1 ) according to any one of the previous claims, wherein the diode device (1 ) is a rectification diode device configured to convert alternating current (AC) or alternating voltage to direct current (DC).

40. Diode device (1 ) according to any one of the previous claims, wherein the diode device (1 ) is a solar energy harvesting diode.

41. Diode device according to any one of the previous claims, wherein the diode device (1) is a THz-cutoff frequency diode.

42. Diode device (1 ) according to any one of the previous claims, wherein the diode device (1 ) is a rectenna diode.

43. Visible-infrared rectenna including at least one nano-antenna and at least one diode device (1 ) according to any one of the previous claims 1 to 42, the at least one diode device (1 ) being coupled to the at least one nano-antenna to rectify, to direct current (DC), an alternating current or voltage provided by the at least one nano-antenna during visible and / or infrared electromagnetic radiation capture by the at least one nano-antenna.

44. Visible-infrared rectenna according to the previous claim, wherein the at least one nanoantenna includes at least arm comprising or consisting solely of graphene to improve coupling efficiency between the at least one nano-antenna and the at least one diode device (1 ).

45. Visible-infrared spectrum solar cell including at least one or a plurality of diode devices (1 ) according to any one of the previous claims 1 to 42; or the visible-infrared rectenna according to any one of the previous claims 43 to 44.

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