Rectifying antenna with MIM diode

Abstract

The invention relates to a rectifier antenna comprising: an antenna (10); a MIIM-type diode 20 having a first metallic layer (21), a first insulating layer (22) made of a first electrical insulator (I1) with electron affinity ϕ1, a second insulating layer (23) made of a second electrical insulator (I2) with electron affinity ϕ2 lower than ϕ1, and a second metallic layer (24). The second electrical insulator (I2) has a dielectric constant εr2 lower than the dielectric constant εr1 of the first electrical insulator (I1), and is a silicon oxide with a thickness between 0.5 and 2 nm.

Description

DOMAINE TECHNIQUE

[0001] The field of the invention is that of rectenna-type electromagnetic radiation detectors with a MIIM diode, in other words, rectifier antennas comprising an electromagnetic radiation-absorbing antenna coupled to an MIIM diode, also called "rectennas". The invention finds application particularly in the fields of infrared or terahertz imaging, thermography, gas detection, and energy conversion. ÉTAT DE LA TECHNIQUE ANTÉRIEURE

[0002] Infrared and terahertz detectors that operate at room temperature can be, for example, bolometer-type thermal detectors. These may consist of an absorbing membrane suspended above a substrate containing a readout circuit, which itself contains a thermistor material whose electrical resistance varies with temperature. However, the performance of these thermal detectors is generally limited by their thermal time constant, which can be on the order of tens of milliseconds.

[0003] Infrared and terahertz detectors can also be rectifier devices comprising a detection antenna coupled to a diode, also called "rectifying antennas" or "rectennas," where the diode can be of the MIM (metal-insulator-metal) or MIIM (metal-insulator-insulator-metal) type. These rectennas can exhibit a much faster response time than bolometer-type thermal detectors, since the transit time of electrons by tunneling through the insulating thin layer of the diode is on the order of femtoseconds to nanoseconds.

[0004] There figure 1A Figure A illustrates the schematic diagram of a rectenna A1, here in the case of an energy conversion application. It consists of an antenna A10 adapted to absorb the incident electromagnetic radiation, and a rectifier element A20 such as a diode, here of the MIM type, electrically coupled to the antenna A10. A DC filter A2 is generally connected in parallel with the diode A20 to retain only the DC component of the rectified AC signal. The operating principle of such a rectenna A1 is as follows: the antenna A10 absorbs the incident electromagnetic radiation and converts it into a high-frequency electrical signal, which is transferred to the input of the diode A20. The diode A20 rectifies the AC electrical signal, and then the DC filter A2 retains only the DC component of the rectified electrical signal, to supply it here to an electrical load A3.

[0005] There figure 1B This illustrates an example of an energy band diagram for a MIM diode rectenna, here in the case of an optical sensing application. Such a rectenna is described in particular in the article by Grover & Moddel entitled "Applicability of Metal / Insulator / Metal (MIM) Diodes to Solar Rectennas," IEEE Journal of Photovoltaics, Vol. 1, no. 1, pp. 78-83, 2011. The MIM diode consists of two metallic layers (metals M1 and M2) with a single insulating layer (electrical insulator I) between them. The diagram depends in particular on the work functions ΨM1 and ΨM2 of metals M1 and M2, the electron affinity ϕI of the insulator I, and the bias voltage VD applied to the MIM diode. Electrons can cross the energy barrier via different conduction mechanisms, for example by Fowler-Nordheim tunneling or by direct tunneling, depending in particular on the heights ϕL and ϕR of the energy barriers.These different types of conduction mechanisms are described in particular in Chiu's article entitled A Review on Conduction Mechanisms in Dielectric Films, Advances in Materials Science and Engineering, vol. 2014, Article ID 578168, 18 pages, 2014. In this example, tunneling conduction is of the Fowler-Nordheim type.

[0006] As indicated in the Grover & Moddel 2011 article, in terms of performance, the MIM diode is sought to exhibit a high responsiveness β, which corresponds to a measure of the rectified DC signal as a function of the incident power. It can be determined from the diode's I(V) characteristic using the relation: β = I" / (2I'), where I' and I" are the first and second derivatives of the electric current as a function of the voltage I(V), at the bias voltage VD. Furthermore, the diode is also sought to have a low dynamic resistance to achieve good impedance matching with the antenna.

[0007] However, it appears that for a MIM diode—that is, a diode with a single insulating layer between two metallic layers—optimizing responsiveness leads to a degradation of the dynamic resistance value, and vice versa. Therefore, it does not seem possible to optimize both the responsiveness and the dynamic resistance of an MIM diode simultaneously. Yet, it appears that a MIIM diode—that is, a diode with two insulating layers having different electronic affinities—overcomes this constraint, making it possible to configure the MIIM diode to exhibit both high responsiveness and low dynamic resistance. This is particularly true when the MIIM diode allows charge carrier conduction via resonant tunneling.

[0008] In this respect, the figure 1C This illustrates an example of an energy band diagram of an infrared rectenna with an MIIM diode configured to allow conduction of charge carriers, here electrons, by resonant tunneling. This type of energy band diagram is described in particular in the article by Grover & Moddel entitled "Engineering the current-voltage characteristics of metal-insulator-metal diodes using double-insulator tunnel barriers", Solid-State Electron. 67, 94-99 (2012), as well as in that of Belkadi et al. entitled "Demonstration of resonant tunneling effects in metal-double-insulator-metal (MI2M) diodes", Nat Commun 12, 2925 (2021).

[0009] Resonant tunneling occurs when electrons pass through insulating layers via a right-angled quantum well located between the two insulating layers. Electrons with energies corresponding to the energy levels of the quasi-bound states in the quantum well can traverse the insulating layers and reach the M2 metallic layer while minimizing reflection, thus producing a higher electric current than in the case of non-resonant tunneling. Note that, in this example, the electrons traverse the first insulating layer via Fowler-Nordheim tunneling and the second insulating layer via direct tunneling. The authors have shown that by using insulators with different electron affinities, it is possible to configure a resonant tunneling MIIM diode to achieve both high responsiveness and low dynamic resistance, which is not possible with a standard MIM diode.

[0010] However, there is a need to further improve the performance of a MIIM type diode rectenna, whether for infrared or terahertz detection applications, or for energy conversion applications. EXPOSÉ DE L'INVENTION

[0011] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to offer a MIIM diode rectenna with improved performance.

[0012] For this purpose, the object of the invention is a rectifier antenna for detecting electromagnetic radiation, comprising: an antenna adapted to absorb electromagnetic radiation; and a Metal-Insulator-Insulator-Metal (MIIM) diode, electrically coupled to the antenna, comprising, successively: a first metallic layer, a first insulating layer made of a first electrical insulator of electronic affinity ϕ 1, a second insulating layer made of a second electrical insulator of electronic affinity ϕ 2 less than ϕ 1, and a second metallic layer.

[0013] According to the invention, the second electrical insulator has a dielectric constant εr2 lower than the dielectric constant εr1 of the first electrical insulator, and is a silicon oxide with a thickness between 0.5 and 2nm.

[0014] Some preferred but not exhaustive aspects of this rectifying antenna are as follows.

[0015] The first electrical insulator can be chosen from Al2O3, ZrO2, HfO2, ZnO and HfAlO, and preferably is HfO2 or ZnO.

[0016] The first insulating layer can have a thickness of between 0.5 and 4nm.

[0017] The first metallic layer, the first insulating layer, the second insulating layer, and the second metallic layer can form a stack with dimensions between 40×40nm and 100×100nm.

[0018] In the diode, each of the said metallic and insulating layers can be continuously in contact with the neighboring layer over its entire surface.

[0019] The rectifier antenna may include an electrical source adapted to apply a non-zero bias voltage VD to the diode.

[0020] The electrical source can be adapted to apply an electrical potential to the first and second metallic layers, with the electrical potential applied to the second metallic layer being greater than that applied to the first metallic layer.

[0021] The first metallic layer can have an electrical potential equal to that of the second metallic layer.

[0022] The rectifier antenna may include a reflector of the electromagnetic radiation of interest, located between a support substrate and the antenna, and spaced from the antenna so as to form a quarter-wave cavity.

[0023] The antenna can be adapted to absorb electromagnetic radiation in the infrared or terahertz range.

[0024] The invention also relates to an optoelectronic device, comprising a rectifier antenna array according to any one of the preceding characteristics, identical to each other.

[0025] The invention also relates to a method for manufacturing a rectifier antenna according to any one of the preceding characteristics, comprising the following steps: fabrication of a first conductive part of the antenna; fabrication of the first metallic layer of the diode, extending over and in contact with the first conductive part of the antenna; fabrication of a first continuous insulating layer, covering the first metallic layer and the first conductive part of the antenna; fabrication of a first opening, located at the level of a so-called proximal end of the first conductive part of the antenna, opening onto the first metallic layer; fabrication of the first insulating layer extending into the first opening and coming into contact with the first metallic layer; fabrication by assisted ion beam deposition of the second insulating layer in a silicon oxide of a thickness between 0.5 and 2nm, extending into the first opening and coming into contact with the first insulating layer; fabrication of the second metallic layer, extending into the first opening and coming into contact with the second insulating layer; fabrication of a second conductive part of the antenna, extending over and in contact with the second metallic layer. BRÈVE DESCRIPTION DES DESSINS

[0026] Other aspects, objectives, advantages, and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1A The figure already described is a schematic view of a diode rectifier antenna coupled to an antenna, according to a prior art example; figure 1B The figure already described illustrates an example of an energy band diagram of a diode MIM rectifier antenna, based on a prior art example; figure 1C The figure already described illustrates an example of an energy band diagram of a diode MIIM rectifier antenna, based on a prior art example; figure 2A and the figure 2B are schematic and partial views, in cross-section ( fig.2A ) and in top view ( fig.2B ), of a MIIM diode rectifier antenna according to one embodiment; the figure 3 illustrates the evolution of the responsiveness β of a MIIM diode as a function of the bias voltage VD, for different examples of electrically insulating materials and insulating layer thicknesses; figures 4A à 4J illustrate different stages of a manufacturing process for a MIIM diode rectifier antenna according to one embodiment. EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERS

[0027] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise stated, the terms "approximately," "around," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean inclusive of the bounds, unless otherwise specified.

[0028] The invention relates to a rectenna-type electromagnetic radiation detector with a MIIM diode, in other words, a rectifier antenna comprising an antenna adapted to absorb electromagnetic radiation coupled to a MIIM diode. In the following description, such a rectifier antenna is referred to as a "rectenna." It can function as an infrared or terahertz detector, or even as a power converter, depending in particular on whether the diode is biased, or not, to a non-zero voltage VD.

[0029] In general, the rectenna antenna can be adapted to absorb electromagnetic radiation of interest across a spectral range, notably from infrared to terahertz. Thus, the antenna can be configured to absorb in the near-infrared (SWIR) range. Short Wavelength IR, (in English) corresponding to a spectral range from approximately 0.8 to 2.7 µm; in the mid-infrared (MWIR, for Middle Wavelength IR, (in English) corresponding to a spectral range from approximately 3 to 5 µm; in the far-infrared (LWIR, for Long Wavelength IR, (in English) corresponding to a spectral range from approximately 7 to 14µm; or even in the terahertz range, which has a spectral range from approximately 0.1 to 1mm (approximately 0.3 to 3THz).

[0030] There figure 2A and the figure 2B are schematic and partial views, in cross-section ( fig.2A ) and in top view ( fig.2B ), of a rectenna according to a mode of realization.

[0031] We define here and for the rest of the description a direct three-dimensional XYZ frame, where the XY plane is parallel to the principal plane of the antenna 10 of the rectenna 1, and where the Z axis is oriented along the thickness of the diode 20 of the rectenna 1. Moreover, the terms "lower" and "upper" are understood as being relative to an increasing positioning along the +Z direction.

[0032] In this example, the Rectenna 1 is an infrared detector whose antenna is adapted to absorb in the LWIR infrared, with a center wavelength of approximately 10 µm. Of course, the Rectenna 1 can be configured to absorb in other infrared spectral ranges, even in the terahertz range.

[0033] Preferably, the described rectenna 1 belongs to a matrix of unit rectennas, identical to each other, connected to an electrical control and reading circuit (ROIC) responsible for biasing the diodes 20 and reading the generated electrical signals.

[0034] In general, the rectenna 1 comprises an antenna 10, the MIIM diode 20, and a DC filter (not shown). Here, it includes a power source to bias the MIIM diode to a non-zero voltage VD (optical detection application). However, in the case of an energy conversion application (e.g., solar cell), the MIIM diode can be unbiased or biased to zero voltage and can be connected to an electrical load.

[0035] Antenna 10 is adapted to absorb incident electromagnetic radiation, here LWIR infrared radiation, and is electrically connected to diode MIIM 20 to transmit to it the electrical signal generated in response to the absorption of the infrared radiation of interest.

[0036] The antenna 10 comprises at least two electrically conductive parts 11, 12, made of at least one absorbing metal, such as Ti, TiN, Al, Au, Pt, among others. The conductive parts 11, 12 are aligned along a principal detection axis X. In this example, the antenna 10 has two conductive parts 11, 12 extending along the same principal axis X, but alternatively (not shown), it may have more conductive parts, for example, four conductive parts, two of which extend along a first principal axis, and two extend along a second principal axis orthogonal to the first axis.

[0037] Antenna 10 can have a spiral, serpentine, dipole, or bowtie shape ( bow-tie (in English). In this example, the antenna 10 is of the bowtie type, also called a butterfly antenna. The two conductive parts 11, 12 have a substantially planar and triangular shape in the XY plane, where the vertices of the triangles are located opposite diode 20 along the vertical axis Z. The antenna 10 has a length L along the principal axis X of approximately λc / 2, where λc is the central wavelength of the LWIR spectral range, for example, approximately 10 µm here. The angular opening of each triangular conductive part 11, 12, defined at the vertices opposite diode 20, can be approximately 60°. Finally, the antenna can have a resistance RA of approximately 100 Ω.

[0038] The two conductive parts 11, 12 are distinct from each other and are electrically connected to each other via diode 20. They are arranged on either side of diode 20 along the principal axis X. Thus, as illustrated by the fig.2A , a lower conductive part 11 is in electrical contact with a lower metallic layer 21 of the diode 20, and an upper conductive part 12 is in electrical contact with an upper conductive layer 24 of the diode 20.

[0039] The MIIM diode 20 is adapted to receive the high-frequency AC electrical signal generated by the antenna 10 in response to the absorption of the electromagnetic radiation of interest, here in the LWIR, and to rectify it to provide a rectified AC electrical signal.

[0040] The diode 20 is formed by a stacking of two metal layers 21, 24, between which are located at least two insulating layers 22, 23. More precisely, the diode 20 comprises the successive stacking of the following layers, which are in contact two by two: the first metal layer 21, the first insulating layer 22, the second insulating layer 23, and the second metal layer 24. In this example, this arrangement is made in the +Z direction, but it could be made in the opposite direction.

[0041] In this example, the stacking of layers 21, 22, 23, 24 is oriented along the vertical axis Z. The lower metal layer 21 is in electrical contact with the proximal end of the conductive part 11 of the antenna 10, and the upper metal layer 24 is in electrical contact with the proximal end of the conductive part 12. By proximal ends, we mean the ends of the conductive parts 11, 12 oriented towards each other.

[0042] Note that, in diode 20, each of the layers 21, 22, 23, 24 extends continuously parallel to the XY plane and is continuously in contact with the neighboring layer(s) over its entire surface. This distinguishes it from the case where one of the layers is formed by distinct lines or grooves, such that the neighboring layer is not in contact with the grooved layer over its entire surface.

[0043] The metallic layer 21 is made of at least one first metal M1, whose work function is denoted ΨM1. It is in contact with the first insulating layer 22. The second metallic layer 24 is made of at least one second metal M2, whose work function is denoted ΨM2. It is in contact with the second insulating layer 23. The metal M1 can be chosen, in particular, from Ti, Cr, TiN, and AlCu, and the metal M2 can be chosen, in this case where M1 is chosen to be different from M2, from Ni, Pt, and Au.

[0044] In the case of an optical detection application, the two metals M1 and M2 can be identical or different in terms of their work functions. However, in the case of an energy conversion application, the work functions ΨM1 and ΨM2 are different. By "different work functions," we mean that the work function ΨM1 of metal M1 differs from the work function ΨM2 of metal M2 by more than 10%. In other words, ΔΨM1M2 / ΨM1 = |ΨM1 - ΨM2| / ΨM1 > 10%. Preferably, the work function ΨM2 is small compared to ΨM1, for example, on the order of 4 eV.

[0045] The first insulating layer 22 is made of an electrically insulating material I1 with electron affinity ϕ1 and dielectric constant εr1, and the second insulating layer 23 is made of an electrically insulating material I2 with electron affinity ϕ2 and dielectric constant εr2. The dielectric constant corresponds to the relative permittivity.

[0046] Insulator I1 has an electron affinity ϕ1 and a dielectric constant εr1 greater than, respectively, the electron affinity ϕ2 and the dielectric constant εr2 of insulator I2. Preferably, insulators I1 and I2 have a relative difference in electron affinity Δϕ / ϕ2 = |ϕ1 - ϕ2| / ϕ2 of at least 50%, or even 100%, 150%, or more. Preferably, insulators I1 and I2 have a relative difference in dielectric constant Δεr / εr2 = |εr1 - εr2| / εr2 of at least 100%, or even 200%, or more.

[0047] The insulator I1 can be an oxide of aluminum, hafnium, zirconium, silicon, zinc, among others, such as Al₂O₃, HfO₂, HfAlO, ZrO₂, ZnO. It is preferably a material with a particularly high dielectric constant (material high-k ) , such as Al 2 O 3 (ε r1 =6-7 ; ϕ 1 =1.5eV), HfO 2 (ε r1 =10-12 ; ϕ 1 =2.5eV), ZrO 2 (ε r1 =15-25 ; ϕ 1 =2.9eV) and ZnO (ε r1 =8.5 ; ϕ 1 =4.2eV), which results in an increase in the asymmetry of diode 20 and a reduction in its dynamic resistance.

[0048] According to the invention, the insulator I2 is a silicon oxide, for example SiO2, with a thickness between 0.5 and 2 nm (insulating layer thickness 23). It is a so-called low-k in the sense that it exhibits a low dielectric constant εr2 equal to approximately 2 (for a thickness on the order of 1nm). Furthermore, it has an electron affinity ϕ2 of 0.9eV.

[0049] The insulating layer 22 has a thickness on the order of a few tenths of a nanometer to a few nanometers, preferably between 0.5 and 4 nm, and more preferably between 1 and 4 nm. Furthermore, as mentioned above, the insulating layer 23 has a thickness between 0.5 and 2 nm. The insulating layers may have the same thickness or different thicknesses.

[0050] The insulating layer 22 is a thin film, meaning a layer produced using conventional microelectronic techniques, including chemical deposition (CVD, ALD, etc.) and physical deposition (PVD, etc.), among others. The insulating layer 23, made of a silicon oxide ranging from 0.5 to 2 nm thick, is a thin film produced by focused ion beam deposition (IBAD). Ion Beam Assisted Deposition, (in English) at room temperature. It is not deposited by very thin film formation techniques such as atomic layer deposition (ALD, for Atomic Layer Deposition, in English).

[0051] Thus, the SiO₂ insulating layer deposited by IBAD at room temperature exhibits good quality, in that its interface has few or no defects such as precursors. These precursors could indeed be present if the layer were deposited by ALD, and could therefore alter the quality of the interface, degrading the electron affinity and thus the β responsiveness of the diode. Furthermore, it should be noted that this silicon oxide insulating layer 23 is not produced by thermal oxidation of an underlying silicon layer, since the underlying layer is the insulating layer 22. Thermal oxidation would also require heating the stack to a high temperature, which can be detrimental to the thermal budget of the readout circuit.

[0052] Preferably, the MIIM diode stack has dimensions in the XY plane between 40nm×40nm and 100nm×100nm, for example, 50nm×50nm. Parts 11 and 12 of the antenna 10 can have a length, along the X-axis, between 2 and 3µm in the case of absorption in the LWIR band. This length can be defined, for each part 11, 12, in the widening region. Note that the fig.2B is very schematic: antenna 10 can have a shape in bow-tie different.

[0053] Rectenna 1 also includes a DC filter (not shown), electrically connected to diode 20, to filter the rectified AC electrical signal and retain only the DC component. The filter is then electrically connected to a circuit for reading the electrical signal (optical detection application) or to an electrical load (energy conversion application).

[0054] An electrical source may be present to electrically bias the diode 20 to a bias voltage VD. For example, the metal layer M1 is grounded while the metal layer M2 is held at an electrical potential UD, which may be zero or non-zero depending on the intended application. Preferably, in the case of an optical detection application, the electrical potential UD applied to the metal layer 24 is positive and higher than that applied to the metal layer 21. The electrical voltage VD may be between approximately 0 and 0.3 V.

[0055] Recall here that the performance of the Rectenna 1 depends in particular on the dynamic resistance RD of diode 20, the asymmetry As D of the I(V) characteristic, and the responsiveness β. The dynamic resistance RD can be determined from the relation RD = 1 / I', where I' is the first derivative of the electric current I as a function of the electric voltage V, at the bias voltage VD. The asymmetry As D can be determined from the relation As D = |I f / I r |, at the bias voltage VD, where I f is the value of the electric current in forward and I r is that of the electric current in reverse. Finally, the responsiveness β has been defined previously and can be determined by the relation: β = I" / (2I').

[0056] Thus, Rectenna 1 comprises a MIIM-type diode where the insulating layer 23 is made of silicon oxide with a thickness of 0.5 to 2 nm, while the insulating layer 22 has a higher electron affinity and dielectric constant than silicon oxide. Due to these characteristics, the MIIM diode 20 exhibits better confinement of the electric field because of the silicon oxide insulating layer 23 (material low-k ) of small thickness, which contributes to increasing the responsiveness and bandwidth of diode 20. In addition, the contrast in electron affinity helps to improve the asymmetry of the I(V) characteristic of diode 20. Furthermore, the insulating layer 22 is preferably made of a material high-k, This allows for optimized dynamic resistance. Furthermore, the fact that the thin silicon oxide is produced by IBAD at room temperature ensures a high-quality oxide with the desired thickness, thus preserving the diode's performance. The Rectenna 1 therefore exhibits improved performance compared to conventional MIIM diode Rectennas.

[0057] As an example, consider an infrared rectenna 1 adapted to absorb in the LWIR, and comprising a MIIM diode 20. The antenna 10 is of the bowtie type and has a total length L on the order of λc / 2 along the principal axis X, where λc is the central wavelength of the LWIR radiation to be detected. To detect a central wavelength λc = 10.6 µm in the case of an underlying dielectric material of refractive index nr beneath the antenna, the wavelength for which the antenna is adapted is λerr = 6.20 µm. In this case, the length L of the bowtie antenna is between approximately 3 and 5 µm, and the length is preferably equal to 4 µm, and the angular opening of the triangular conducting parts 11, 12 of the antenna 10 is on the order of 60°.The antenna 10 is located above a metallic reflector 35, and is vertically separated from it by a thickness on the order of λc / 4n, where n is the refractive index of the medium 37 separating the antenna 10 from the reflector 35. Here, this medium 37 is a silicon oxide with a thickness on the order of approximately 1 µm. This forms a quarter-wave cavity which improves the absorption rate of the antenna 10.

[0058] There figure 3 illustrates an example of the evolution of the responsivity β of the MIIM diode as a function of the bias voltage VD.

[0059] Several pairs of insulating materials I1, I2 are illustrated. In these different cases, the metal layer 21 is made of TiN (Ψ M1 = 4.3 eV) and the metal layer 24 is made of Ni (Ψ M2 = 5 eV). The diode has dimensions of 100 nm × 100 nm in the XY plane.

[0060] First, we measure the evolution of the β responsiveness of a diode when the diode's insulator I2 is not made of silicon dioxide (i.e., a conventional MIIM diode). We consider a pair of insulators where I1 is 1 nm thick HfO2 and I2 is 1 nm thick Al2O3. We observe that the β responsiveness has a very low value, close to 0 V, for a voltage VD of 0.1 V. However, when the thicknesses increase to 2 nm for HfO2 and 0.5 nm for Al2O3, the β responsiveness increases to approximately 2 V for a voltage VD of 0.1 V.

[0061] The evolution of the β responsiveness of a diode 20 is then measured according to an embodiment of the invention, in the case where the diode's insulator I2 is made of silicon dioxide with a thickness between 0.5 and 2 nm. First, a pair of insulators is considered where I1 is HfO2, 1 nm thick, and I2 is SiO2, 1 nm thick. It is observed that the β responsiveness has a value close to 4 V⁻¹ for a voltage VD of 0.1 V. Compared with the previous case where I2 is Al2O3 and the thicknesses are identical, the β responsiveness has increased from a near-zero value to approximately 4 V⁻¹. The improvement is therefore very significant.

[0062] This value can be improved by adjusting the thicknesses. For example, for a pair of insulators where I1 is 0.5 nm thick HfO₂ and I2 is 1 nm thick SiO₂, the β responsiveness increases to over 5 V⁻¹ for the same voltage value VD. Note that other materials also exhibit high responsiveness; for instance, with the same pair of insulators where I1 is 0.5 nm thick Al₂O₃ and I2 is 1 nm thick SiO₂, the β responsiveness is approximately 2.5 V⁻¹, which is significantly higher than in a conventional diode where the insulator I2 is not silicon oxide. Furthermore, it should be noted that making an insulating layer 23 out of a thinner silicon oxide, for example 0.5nm, will result in a decrease in dynamic resistance and an increase in the β responsivity of the diode.

[0063] THE figures 4A à 4J illustrate different stages of a manufacturing process for a rectenna 1 according to one embodiment. The rectenna 1 is here adapted to absorb electromagnetic radiation of interest in the LWIR. Only a single rectenna is shown here, but preferably, the process involves the fabrication of an array of identical rectennas on the same reading substrate 31.

[0064] As previously mentioned, the insulating layer 23 is made of silicon oxide with a thickness of 0.5 to 2 nm by focused ion beam deposition (IBAD, for Ion Beam Assisted Deposition, (in English) at room temperature and not by atomic layer deposition (ALD, for Atomic Layer Deposition, (in English), and even less so by thermal oxidation.

[0065] With reference to the fig.4A , a readout substrate 31 is provided, containing a readout and control circuit (ROIC), for example of CMOS type, adapted here to electrically bias the diode and to read the rectified electrical signal from the rectenna in response to the absorption of LWIR radiation.

[0066] The reading substrate 31 is covered with a lower insulating layer 32, made of an insulating material such as silicon oxide. First conductive vias 33 are then made through the lower insulating layer 32 and connected to connection pads of the reading substrate 31 (not shown), followed by first electrical connection pads 34 in contact with the conductive vias 33.

[0067] With reference to the fig.4B Next, the reflector 35 and intermediate connection pads 36 are fabricated. This is achieved by depositing a layer of at least one metallic material, which is then structured by lithography and localized etching to form the reflector 35 and the connection pads 36. The metallic layer can be a multilayer, for example, of the Ti / TiN / AlCu or Ti / TiN / AlSi type. The AlCu or AlSi layer can be at least 80 nm thick, for example, 300 nm. The connection pads 36 are in electrical contact with the connection pads 34.

[0068] With reference to the fig.4C An intermediate insulating layer 37, made of an insulating material such as silicon oxide, is deposited to define the quarter-wave cavity with the antenna. SiO₂ can be deposited by plasma-enhanced physical vapor deposition (PECVD), with a thickness, for example, between 0.3 and 2 µm, or 1.2 µm, at a deposition temperature of 400°C or lower to comply with the thermal budget of the CMOS readout circuit. A chemical-mechanical polishing step can then be performed to remove excess material and flatten the intermediate insulating layer 37 to a thickness of approximately 1 µm (the optical cavity has a thickness of λ / 4n, where n is the refractive index of the medium forming the optical cavity). Secondary conductive vias 38 are then made through the intermediate insulating layer 37, making contact with the connection pads 36.

[0069] With reference to the fig.4D and to the fig.4E Next, the lower conductive part 11 of the antenna and the lower metallic layer 21 of the diode are fabricated. This is achieved by depositing a layer of at least one metallic material, which is then structured by lithography and etching. The layer is preferably formed from a metallic multilayer, for example, Ti / AlCu / TiN. This multilayer forms both the lower conductive part 11 of the antenna and the lower metallic TiN layer 21 of the diode. The intermediate AlCu layer is preferably thicker than 80 nm to ensure the quality and continuity of the layer. An upper connection pad 39, intended to bias the upper conductive part of the antenna, is also formed from the multilayer.Next, an upper insulating layer 40 is deposited, for example in a TEOS type silicon oxide, which is planarized to free the upper face of the metal layer 21 of the diode as well as that of the upper connection pad 39.

[0070] With reference to the fig.4F , then an insulating layer 41 is deposited, covering the metallic layer 21, the connection pad 39, and the upper insulating layer 40. This insulating layer 41 can be made of SiO 2 with a thickness of between 20 and 100nm approximately.

[0071] With reference to the fig.4G , a localized opening 50 is made through the insulating layer 41, which opens at an edge of the metallic layer 21 where the diode will be located. This opening 50 can be made by electron beam photolithography ( e-beam, (in English), and can have a dimension in the XY plane of the order of 40nm to 100nm. The insulating layer 41 is etched with an etching stop on or in the metallic layer 21.

[0072] The first insulating layer 22 is then produced, here by atomic layer deposition (ALD) at a temperature between approximately 200 and 400°C, for example 300°C. It has a thickness of approximately 1 to 3 nm. A material is preferably chosen high-k exhibiting a high electron affinity, for example HfO2 or ZnO. This insulating layer 22 continuously covers the insulating layer 41 as well as the bottom and side wall of the opening 50. It is therefore in contact with and completely covers the metallic layer 21.

[0073] The second insulating layer 23 is then created. It is made of silicon oxide, here SiO2, with a thickness between 0.5 and 2 nm. It is therefore a material low-k (εr2 = approx. 2) having a low electron affinity (ϕ2 = 0.9 eV). In order to obtain a good quality SiO2 insulating layer at the interface, it is produced by IBAD at room temperature (approx. 25°C). This insulating layer 23 continuously covers the insulating layer 22, both above the insulating layer 41 and in the opening 50. It is therefore in contact with and completely covers the insulating layer 22.

[0074] The oxide deposition is carried out using a SiO₂ ceramic target. Oxygen can be introduced into the deposition chamber via two sources, referred to as Dep and Assist. When no voltage is applied to the Assist source, radical oxidation occurs. In other words, the O⁻ radicals are ejected into the chamber with very low kinetic energy. Conversely, when the O⁻ radicals are ejected using the Assist source as well, ionic oxidation occurs, and this is referred to as ion beam-assisted deposition (IBAD). Preferably, the insulating SiO₂ layer 23 is produced by IBAD, as this results in a very thin (here 0.5 nm) and high-quality SiO₂ deposit on the underlying insulating layer 22.

[0075] With reference to the fig.4H , a second opening 51 is made locally through the insulating layer 23 in SiO 2, the insulating layer 22, the insulating layer 41, to open onto the connection pad 39 (here on the metallic layer 21).

[0076] The metallic layer 24 of the diode 20 is then fabricated. It is deposited so as to cover the insulating layer 23 made of SiO₂ in the aperture 50. It also extends beyond the aperture 50, therefore above the insulating layer 41, and also into the second aperture 51. This metallic layer 24 can be, for example, a metal with a low work function, for example on the order of 4 eV, such as Ti, Cr, or TiN, among others. It can be fabricated by evaporation or by CVD or ALD deposition.

[0077] Next, a top metallic layer 25 is deposited to form the upper part 12 of the antenna 10. This layer 25 covers and is in contact with the metallic layer 24 at the diode 20, as well as at the connection point 39. This layer can be made of AI, Au, Pt, Ni, Cr, among others.

[0078] With reference to the figure 4I and to the figure 4J The metallic layer 25 is structured to form the upper part 12 of the antenna 10 by photolithography and localized etching. Here, the metallic layer 24, the SiO₂ insulating layer 23, and the insulating layer 22 are also etched, with the etching stopped at the TEOS insulating layer 41. The diode 20 is thus biased by the two lower parts 11 and the upper part 12 of the antenna 10 and by the conductive vias 38.

[0079] Thus, a rectenna 1 is obtained, consisting of a butterfly-type antenna 10 and a MIIM diode 20 located between the two vertices of the triangular conductive parts of the antenna 10. The diode 20 is biased by means of conductive vias 38 extending between the conductive parts 11 and 12 of the antenna 10 and the readout circuit. Furthermore, the antenna 10 is vertically separated from a reflector 35, thus forming a quarter-wave cavity that optimizes the absorption of LWIR radiation. Since the MIIM diode 20 contains a high-quality silicon oxide insulating layer 23, here SiO2, with a thickness of 0.5 to 2 nm, deposited by IBAD, the diode 20 exhibits improved performance, particularly in terms of responsiveness.

[0080] Specific embodiments have just been described. Different variations and modifications will be apparent to those skilled in the art.

Claims

1. Rectifying antenna (1) for detecting electromagnetic radiation, comprising: ∘ an antenna (10), adapted to absorb electromagnetic radiation; ∘ a Metal-Insulator-Insulator-Metal (MIIM) diode (20), electrically coupled to the antenna (10), comprising, successively: a first metallic layer (21), a first insulating layer (22) made of a first electrical insulator (I1) with electronic affinity ϕ1, a second insulating layer (23) made of a second electrical insulator (I2) with electronic affinity ϕ2 lower than ϕ1, and a second metallic layer (24); ∘ characterized in that the second electrical insulator (I2) has a dielectric constant ε r2 less than the dielectric constant ε r1 of the first electrical insulator (I1), and is a silicon oxide with a thickness between 0.5 and 2nm.

2. Rectifying antenna (1) according to claim 1, wherein the first electrical insulator (I1) is selected from Al2O3, ZrO2, HfO2, ZnO and HfAlO, and preferably is HfO2 or ZnO.

3. Rectifying antenna (1) according to claim 1 or 2, wherein the first insulating layer (22) has a thickness between 0.5 and 4nm.

4. Rectifying antenna (1) according to any one of claims 1 to 3, wherein the first metallic layer (21), the first insulating layer (22), the second insulating layer (23), and the second metallic layer (24) form a stack of dimensions between 40×40nm and 100×100nm.

5. Rectifying antenna (1) according to any one of claims 1 to 4, in which, in the diode (20), each of said metallic (21, 24) and insulating (22, 23) layers is continuously in contact with the neighboring layer over its entire surface.

6. Rectifying antenna (1) according to any one of claims 1 to 5, comprising an electrical source adapted to apply a bias voltage V D non-zero at diode (20).

7. Rectifying antenna (1) according to claim 6, wherein the electrical source is adapted to apply an electrical potential to the first and second metallic layers (21, 24), the electrical potential applied to the second metallic layer (24) being greater than that applied to the first metallic layer (21).

8. Rectifying antenna (1) according to any one of claims 1 to 5, wherein the first metallic layer (21) has an electrical potential equal to that of the second metallic layer (24).

9. Rectifying antenna (1) according to any one of claims 1 to 8, comprising a reflector (35) of the electromagnetic radiation of interest, located between a support substrate and the antenna (10), and spaced from the antenna (10) so as to form a quarter-wave cavity.

10. Rectifying antenna (1) according to any one of claims 1 to 9, wherein the antenna (10) is adapted to absorb electromagnetic radiation in the infrared or terahertz range.

11. Optoelectronic device, comprising a rectifier antenna array (1) according to any one of claims 1 to 10, identical to each other.

12. A method for manufacturing a rectifier antenna (1) according to any one of claims 1 to 10, comprising the following steps: ∘ making a first conductive part (11) of the antenna (10); ∘ making the first metallic layer (21) of the diode (20), extending over and in contact with the first conductive part (11) of the antenna (10); ∘ making a first continuous insulating layer (41), covering the first metallic layer (21) and the first conductive part (11) of the antenna (10); ∘ making a first opening (50), located at a so-called proximal end of the first conductive part (11) of the antenna (10), opening onto the first metallic layer (21); ∘ creation of the first insulating layer (22) extending into the first opening (50) and coming into contact with the first metallic layer (21);• Fabrication by ion beam assisted deposition (IBAD) of the second insulating layer (23) in a silicon oxide with a thickness between 0.5 and 2 nm, extending into the first opening (50) and coming into contact with the first insulating layer (22); • Fabrication of the second metallic layer (24), extending into the first opening (50) and coming into contact with the second insulating layer (23); • Fabrication of a second conductive part (12) of the antenna (10), extending over and in contact with the second metallic layer (24).

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