MIIM diode rectifier antenna

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 an 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. Figure for the abstract: Fig. 2A

Description

Title of the invention: MIIM diode rectifier antenna technical field

[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. PREVIOUS STATE OF THE ART

[0002] Infrared and terahertz detectors that operate at room temperature can be, for example, bolometer-type thermal detectors. These can include an absorbing membrane suspended above a substrate containing a readout circuit, which itself contains a thermistor material whose electrical resistance varies with its temperature rise. 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 response time much faster than that of 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] Figure 1A 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 filters it. DC A2 retains only the DC component of the rectified electrical signal, to supply it here to an electrical load A3.

[0005] Figure IB illustrates an example of an energy band diagram of 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 comprises two metallic layers (metals M1 and M2) between which lies a single insulating layer (electrical insulator I). The diagram depends in particular on the work functions WMi and WM2 of metals M1 and M2, the electron affinity 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 q>L and q>R 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 article by Grover & Moddel 2011, in terms of performance, the MIM diode is required to exhibit high responsiveness [3], which corresponds to a measurement of the rectified DC signal as a function of the incident power. This can be determined from the diode's I(V) characteristic using the relation: [3 = 1'7(21'), where I' and I” are the first and second derivatives of the electric current as a function of the electric voltage I(V), at the bias voltage VD. Furthermore, the diode is also required to exhibit 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 located between the 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. However, it appears that a MIIM diode, that is, a diode with two insulating layers having different electronic affinities, makes it possible to overcome this constraint, so that it is possible to configure the MIIM diode to exhibit both high responsiveness and low dynamic resistance. This is particularly the case when the MIIM diode allows charge carrier conduction by resonant tunneling.

[0008] In this respect, [Fig. IC] 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 by Belkadi et al. entitled Demonstration of resonant tunneling effects in metal-double-insulator-metal (MI2 M) diodes, Nat Commun 12, 2925 (2021).

[0009] Resonant tunneling occurs when electrons pass through the insulating layers via a right-angled quantum well located between the two insulating layers. Electrons whose energy corresponds to the energy levels of the quasi-bound states of the quantum well can pass through the insulating layers and reach the metallic layer M2 while minimizing reflection, thus producing a higher electric current than in the case of non-resonant tunneling. Note that, in this example, the electrons pass through the first insulating layer by Fowler-Nordheim tunneling, and the second insulating layer by direct tunneling.The authors have shown that by using insulators with different electronic affinities, it is possible to configure a resonant tunneling MIIM-type diode to obtain both high responsiveness and low dynamic resistance, which is not possible to obtain in the case of a 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. Description of the 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 q>i, a second insulating layer made of a second electrical insulator of electronic affinity q>2 less than q>i, and a second metallic layer.

[0013] According to the invention, the second electrical insulator has a dielectric constant er2 lower than the dielectric constant er[ of the first electrical insulator, and is a silicon oxide with a thickness between 0.5 and 2nm.

[0014] Some preferred but not limiting aspects of this rectifying antenna are the following.

[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 may 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 40x40nm and 100x100nm.

[0018] In the diode, each of 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, the electrical potential applied to the second metallic layer being greater than that applied to the first metallic layer.

[0021] The first metallic layer may 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: - creation 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; - creation of a first continuous insulating layer, covering the first metallic layer and the first conductive part of the antenna; - creation of a first opening, located at the level of a so-called proximal end of the first conductive part of the antenna, leading to the first metallic layer; - creation of the first insulating layer extending into the first opening and coming into contact with the first metallic layer; - creation by ion beam assisted 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; - creation of the second metallic layer, extending into the first opening and coming into contact with the second insulating layer; - creation of a second conductive part of the antenna, extending over and in contact with the second metallic layer. Brief description of the drawings

[0026] Other aspects, objects, advantages and features of the invention will become more apparent 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:

[0027] [Fig.1A], already described, is a schematic view of a diode rectifier antenna coupled to an antenna, according to an example of the prior art;

[0028] Fig. 1B, already described, illustrates an example of an energy band diagram of a MIM diode rectifier antenna, according to an example of the prior art;

[0029] Fig. 1C, already described, illustrates an example of an energy band diagram of a diode rectifier antenna MIIM, according to an example of the prior art;

[0030] [Fig.2A] and [Fig.2B] are schematic and partial views, in cross-section ([Fig.2A]) and in top view ([Fig.2B]), of a rectifier antenna with MIIM diode according to an embodiment;

[0031] Fig. 3 illustrates an evolution of the responsivity [3 of a MIIM diode as a function of the bias voltage VD, for different examples of electrical insulating materials and thicknesses of insulating layers;

[0032] Figures 4A to 4J illustrate different stages of a manufacturing process for a MIIM diode rectifier antenna according to one embodiment.

[0033] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0034] In the figures and in the following description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to prioritize the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and can 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 that the limits are inclusive, unless otherwise stated.

[0035] The invention relates to a rectenna-type electromagnetic radiation detector with an MIIM diode, in other words, a rectifier antenna comprising an antenna adapted to absorb electromagnetic radiation coupled to an 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.

[0036] In general, the rectenna antenna can be adapted to absorb electromagnetic radiation of interest in a spectral range extending in particular from the infrared to the terahertz. Thus, the antenna can be configured to absorb in the near-infrared (SWIR, for Short Wavelength IR) corresponding to a spectral range from approximately 0.8 to 2.7 pm; in the mid-infrared (MWIR, for Middle Wavelength IR) corresponding to a spectral range from approximately 3 to 5 pm; in the far-infrared (LWIR, for Long Wavelength IR) corresponding to a spectral range from approximately 7 to 14 pm; or even in the terahertz, the spectral range of which is from approximately 0.1 to 1 mm (approximately 0.3 to 3 THz).

[0037] Fig. 2A and Fig. 2B are schematic and partial views, in cross-section (Fig. 2A) and in top view (Fig. 2B), of a rectenna according to an embodiment.

[0038] Here and for the remainder of the description, a three-dimensional direct frame XYZ is defined, 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. Furthermore, the terms "lower" and "upper" are understood as being relative to an increasing positioning along the +Z direction.

[0039] 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 1 Opm. Of course, the Rectenna 1 can be configured to absorb in other infrared spectral ranges, even in the terahertz range.

[0040] 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.

[0041] In general, the rectenna 1 comprises an antenna 10, the MIIM diode 20 and a DC filter (not shown). Here it includes an electrical source for biasing The MIIM diode operates at a non-zero voltage VD (optical detection application). Conversely, in the case of an energy conversion application (e.g., solar cell), the MIIM diode can be unbiased or biased at zero voltage, and can be connected to an electrical load.

[0042] The antenna 10 is adapted to absorb the incident electromagnetic radiation, here LWIR infrared radiation, and is electrically connected to the diode MIIM 20 to transmit to it the electrical signal generated in response to the absorption of the infrared radiation of interest.

[0043] 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.

[0044] The antenna 10 can be spiral, serpentine, dipole, or bow-tie shaped. In this example, the antenna 10 is of the bow-tie 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 Xc / 2, where Xc is the central wavelength of the LWIR spectral range, for example, here approximately 1 Opm. The angular aperture 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.

[0045] The two conductive parts 11, 12 are distinct from each other, and are electrically connected to each other via the diode 20. They are arranged on either side of the diode 20 along the main axis X. Thus, as illustrated in [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.

[0046] 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.

[0047] The diode 20 is formed by a stacking of the 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.

[0048] 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.

[0049] Note that, in the diode 20, each of the layers 21, 22, 23, 24 extends parallel to the XY plane continuously 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.

[0050] The metallic layer 21 is made of at least one first metal M1, whose work function is denoted WMi. 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 WM2. 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 the case here where M1 is chosen to be different from M2, from Ni, Pt, and Au.

[0051] In the case of an optical detection application, the two metals M1 and M2 may be identical or different in terms of their work output. However, in the case of an energy conversion application, the work outputs WMi and WM2 are different from each other. By "different work outputs," we mean that the work output of metal M1 has a relative difference of 9¼ with respect to the work output WM2 of metal M2 greater than 10%. In other words, we have AWMiM2 / vPMi = IWMrW nJAPmi > 10%. Preferably, the work output WM2 is low compared to WMi, for example, on the order of 4 eV.

[0052] The first insulating layer 22 is made of an electrically insulating material II with electron affinity q>i and dielectric constant er[, and the second insulating layer 23 is made of an electrically insulating material 12 with electron affinity q>2 and dielectric constant er2. The dielectric constant corresponds to the relative permittivity.

[0053] Insulator II has an electron affinity qi and a dielectric constant er1 greater than, respectively, the electron affinity q2 and the dielectric constant er2 of insulator 12. Preferably, insulator II and insulator 12 have a relative difference in electron affinity Aq / q2 = qq / q2 of at least 50%, or even 100%, 150%, or more. Preferably, insulator II and insulator 12 have a relative difference in dielectric constant Ae / e1 = qi / er2 of at least 100%, or even 200%, or more.

[0054] The insulator II can be an oxide of aluminium, hafnium, zirconium, silicon, zinc among others, such as for example Al2O3, HfO2, HfAlO, ZrO2, ZnO. It is preferably a material with a particularly high dielectric constant (high-k material), such as for example Al2O3 (er[=6-7 ; q>i=1.5eV), HfO2 (eri=10-12 ; q>i=2.5eV), ZrO2 (eri=15-25 ; q>i=2.9eV) and ZnO (eri=8.5 ; q>i=4.2eV), which results in an increase in the asymmetry of the diode 20 and a reduction in its dynamic resistance.

[0055] According to the invention, the insulator 12 is a silicon oxide, for example SiO2, with a thickness between 0.5 and 2 nm (thickness of the insulating layer 23). It is a so-called low-k material in the sense that it has a low dielectric constant er2 equal to approximately 2 (for a thickness on the order of Inm). Furthermore, it has an electron affinity q>2 of 0.9 eV.

[0056] 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 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.

[0057] The insulating layer 22 is a thin film, that is, a layer produced by 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 with a thickness of 0.5 to 2 nm, is a thin film produced by focused ion beam deposition (IBAD) at room temperature. It is not deposited by very thin film formation techniques such as atomic layer deposition (ALD).

[0058] Thus, the SiO2 insulating layer deposited by IB AD at room temperature exhibits good quality, in the sense that its interface has few or no defects such as precursors. These could indeed be present if the layer were deposited by ALD, and therefore could alter the quality of the interface and thus degrade the electronic affinity and therefore the responsiveness [3 of the diode. Furthermore, note that this insulating layer 23 in silicon oxide is not made by thermal oxidation of an underlying silicon layer, since the underlying layer here is the insulating layer 22. Thermal oxidation would also require heating the stack to a high temperature, which can be detrimental in terms of the thermal budget of the readout circuit.

[0059] Preferably, the MIIM diode stack has dimensions in the XY plane between 40 nm x 40 nm and 100 nm x 100 nm, for example, 50 nm x 50 nm. Parts 11 and 12 of the antenna 10 can have a length, along the X-axis, of between 2 and 3 pm 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 [Fig. 2B] is very schematic: the antenna 10 can have a different bowtie shape.

[0060] Rectenna 1 also includes a DC filter (not shown), electrically connected to diode 20, so as to filter the rectified AC electrical signal to 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).

[0061] 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 brought to 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.

[0062] It should be recalled here that the performance of the rectenna 1 depends in particular on the dynamic resistance RD of the diode 20, the asymmetry AsD of the I(V) characteristic, and the responsiveness [3]. The dynamic resistance RD can be determined from the relation RD = 1 / 1', 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 AsD can be determined from the relation AsD = IIf / Ir, at the bias voltage VD, where If is the value of the electric current in forward and Ir is that of the electric current in reverse. Finally, the responsiveness [3] has been defined previously and can be determined by the relation: [3] = 1'7(21').

[0063] Thus, the rectenna 1 comprises a MIIM-type diode where the insulating layer 23 is made of a silicon oxide with a thickness of 0.5 to 2 nm, while the layer The insulating layer 22 exhibits higher electron affinity and dielectric constant than silicon oxide. Due to these characteristics, the MIIM diode 20 provides better electric field confinement thanks to the thin silicon oxide insulating layer 23 (low-k material), which contributes to increased responsiveness and bandwidth of diode 20. Furthermore, the contrast in electron affinity helps to improve the asymmetry of the I(V) characteristic of diode 20. In addition, the insulating layer 22 is preferably made of a high-k material, which optimizes dynamic resistance. Finally, the fact that the thin silicon oxide is produced by IB AD at room temperature ensures a high-quality oxide of the desired thickness, thus preserving the diode's performance.The Rectenna 1 therefore offers improved performance compared to conventional MIIM diode Rectennas.

[0064] By way of 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 Xc / 2 along the principal axis X, where Xc is the central wavelength of the LWIR radiation to be detected. To detect a central wavelength Xc = 10.6 pm in the case of the presence of an underlying dielectric material of index nr under the antenna, the wavelength for which the antenna is adapted is Xeff = 6.20 pm. In this case, the length L of the bowtie antenna is between approximately 3 and 5 pm, and the length is preferably equal to 4 pm, 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 Xc / 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 Ipm. This forms a quarter-wave cavity which improves the absorption rate by the antenna 10.

[0065] Fig. 3 illustrates an example of the evolution of the responsivity [3 of the MIIM diode as a function of the bias voltage VD.

[0066] Several pairs of insulating materials II, 12 are illustrated. In these different cases, the metal layer 21 is made of TiN (WM1 = 4.3 eV) and the metal layer 24 is made of Ni (WM2 = 5 eV). The diode has dimensions of 100 nm x 100 nm in the XY plane.

[0067] First, the evolution of the responsivity [3] of a diode is measured in the case where the insulator 12 of the diode is not made of silicon oxide (i.e., a conventional MIIM diode): a pair of insulators is thus considered, where II is HfO2 of thickness Inm and 12 is Al2O3 of thickness Inm. It is noted that the responsivity [3] has a very low value, close to 0 V1, for a voltage VD of 0.1 V. On the other hand, in the case where the thicknesses increase to 2nm for HfO2 and to 0.5 nm for Al2O3, the responsivity [3] increases to approximately 2 V for a voltage VD of 0.1 V.

[0068] The evolution of the responsivity [3] of a diode 20 is then measured according to an embodiment of the invention, in the case where the insulator 12 of the diode is made of silicon oxide with a thickness between 0.5 and 2 nm. First, a pair of insulators is considered, where II is HfO2 with a thickness of 1 nm and 12 is SiO2 with a thickness of 1 nm. It is observed that the responsivity [3] has a value close to 4 V1 for a voltage VD of 0.1 V. Compared with the previous case where 12 is Al2O3 and the thicknesses are identical, it is observed that the responsivity [3] has increased from a value close to zero to approximately 4 V1. The improvement is therefore very significant.

[0069] This value can be improved by adjusting the thicknesses. Thus, for a pair of insulators where II is HfO2 0.5 nm thick and 12 is SiO2 1 nm thick, the responsivity [3] increases to more than 5 V for the same voltage value VD. Note that other materials also exhibit high responsiveness, such as, for example, with the pair of insulators where II is Al2O3 0.5 nm thick and 12 is SiO2 1 nm thick, the responsivity [3] is approximately 2.5 V, therefore much higher than in the case of a conventional diode where the insulator 12 is not a 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 responsivity [3 of the diode.

[0070] Figures 4A to 4J illustrate different steps of a process for manufacturing 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 manufacturing an array of identical rectennas on the same reading substrate 31.

[0071] As previously stated, the insulating layer 23 is made of a silicon oxide with a thickness of 0.5 to 2nm by focused ion beam deposition (IBAD) at room temperature and not by atomic layer deposition (ALD), and even less by thermal oxidation.

[0072] With reference to [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.

[0073] The reading substrate 31 is covered with a lower insulating layer 32, made of an insulating material such as silicon oxide. Then, through the lower insulating layer 32, first conductive vias 33, connected to connection pads of the reading substrate 31 (not shown), then first electrical connection pads 34 in contact with the conductive vias 33.

[0074] With reference to [Fig. 4B], the reflector 35 and intermediate connection pads 36 are then produced. This is done by depositing a layer of at least one metallic material, which is 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 have a thickness of at least 80 nm, for example, 300 nm. The connection pads 36 are in electrical contact with the connection pads 34.

[0075] With reference to [Fig. 4C], an intermediate insulating layer 37, made of an insulating material such as silicon oxide, is deposited to subsequently define the quarter-wave cavity with the antenna. SiO2 can thus be deposited by plasma-enhanced physical vapor deposition (PECVD), with a thickness, for example, between 0.3 and 2 pm, for example 1.2 pm, at a deposition temperature less than or equal to 400°C to respect the thermal budget of the CMOS readout circuit. A chemical-mechanical polishing step can then be carried out to remove excess material and planarize the intermediate insulating layer 37 to a thickness of approximately 1 pm (the optical cavity has a thickness of X / 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.

[0076] With reference to [Fig. 4D] and [Fig. 4E], the lower conductive part 11 of the antenna and the lower metallic layer 21 of the diode are then 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 of 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. .

[0077] With reference to [Fig.4F], an insulating layer 41 is then deposited, covering the metallic layer 21, the connecting pad 39, and the upper insulating layer 40. This insulating layer 41 can be made of SiO2 with a thickness of between 20 and approximately 100nm.

[0078] With reference to [Fig. 4G], a localized aperture 50 is made through the insulating layer 41, opening at an edge of the metallic layer 21 where the diode will be located. This aperture 50 can be made by electron beam photolithography (e-beam) and can have a dimension in the XY plane on the order of 40 nm to 100 nm. The insulating layer 41 is etched with a stop on or within the metallic layer 21.

[0079] 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 high-k material with high electron affinity is preferably chosen, 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.

[0080] The second insulating layer 23 is then produced. It is formed from a silicon oxide, here SiO2, with a thickness between 0.5 and 2 nm. It is therefore a low-k material (er2=2 approx.) having a low electron affinity ( <p2=0.9eV). De manière à obtenir une couche isolante en SiO2 de bonne qualité à l’interface, elle est réalisée par IB AD à température ambiante (25°C env.). Cette couche isolante 23 recouvre continûment la couche isolante 22, tant au-dessus de la couche isolante 41 que dans l’ouverture 50. Elle est donc au contact et recouvre entièrement la couche isolante 22.

[0081] The oxide deposition is carried out using a SiO2 ceramic target. In the deposition frame, oxygen can be introduced by 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, since this yields SiO2 deposited on the underlying insulating layer 22 that is very thin (here 0.5 nm) and of very high quality.

[0082] With reference to [Fig.4H], a second opening 51 is made locally through the insulating layer 23 in SiO2, the insulating layer 22, the insulating layer 41, to open onto the connection pad 39 (here on the metallic layer 21).

[0083] The metallic layer 24 of the diode 20 is then produced. It is deposited so as to cover the insulating layer 23 made of SiO2 in the aperture 50. It extends Here too, outside the aperture 50, therefore above the insulating layer 41, but also within 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, TiN, among others. It can be produced by evaporation or by CVD or ALD deposition.

[0084] 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 pad 39. This layer can be made of Al, Au, Pt, Ni, Cr, among others.

[0085] With reference to [Fig. 41] and [Fig. 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.

[0086] Thus, a rectenna 1 is obtained, formed of a butterfly-type antenna 10 and a MIIM diode 20 located between the two vertices of the triangular conducting parts of the antenna 10. The diode 20 is biased by means of conducting vias 38 extending between the conducting parts 11, 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 the high-quality silicon oxide insulating layer 23, here SiO2, with a thickness of 0.5 to 2 nm, deposited by IB AD, the diode 20 exhibits improved performance, particularly in terms of responsiveness.

[0087] Specific embodiments have just been described. Various variants and modifications will be apparent to those skilled in the art.

Claims

Demands

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 (II) of electronic affinity q>i, a second insulating layer (23) made of a second electrical insulator (12) of electronic affinity q>2 less than q>i, and a second metallic layer (24); • characterized in that the second electrical insulator (12) has a dielectric constant er2 less than the dielectric constant eri of the first electrical insulator (II), 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 (II) 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 40x40nm and 100x100nm.

5. Rectifying antenna (1) according to any one of claims 1 to 4, wherein, 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 non-zero bias voltage VD to the diode (20).

7. Rectifying antenna (1) according to claim 6, wherein the electric source is adapted to apply an electric potential to the first and second metal layers (21, 24), the electric potential applied to the second metal layer (24) being greater than that applied to the first metal 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); production of the first insulating layer (22) extending into the first opening (50) and coming into contact with the first metallic layer (21); production by ion beam assisted deposition (IBAD) of the second insulating layer (23) in a silicon oxide of a thickness between 0.5 and 2nm, extending into the first opening (50) and coming into contact with the first insulating layer (22); production of the second metallic layer (24), extending into the first opening (50) and coming into contact with the second insulating layer (23); production 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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