Broadband thermal detector with multiple quarter-wave cavities.

Abstract

To provide a thermal detector having a broadband absorption spectrum while maintaining uniformly high absorption across the entire spectral band of detection.SOLUTION: The invention relates to a thermal detector with a suspended absorbent membrane, which has at least two absorbers (31, 32). The second absorber (32) is designed to absorb the electromagnetic radiation in a spectral sub-band Δλ2 of a predefined spectral band Δλtot, centered on a wavelength λc2. Moreover, it is spaced from a reflector (12) by a value h2 equal to λc2 / 4neq2 so as to form therewith a quarter-wave cavity C2 for the wavelength λc2, the spectral sub-band Δλ2 being centered on the wavelength λc2 which is equal to λc1 / 2±2 μm. Furthermore, the first and second absorbers (31, 32) have total surface areas such that a surface area ratio S2 / S1 is between 0.5 and 3.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, for example infrared or terahertz, having at least one thermal detector with an absorbing film suspended above a readout substrate. The invention is particularly applicable to the fields of infrared imaging, thermography and, inter alia, gas detection. [Background technology]

[0002] An apparatus for detecting electromagnetic radiation can include a matrix of thermal detectors, each having a film designed to absorb the electromagnetic radiation to be detected and including a thermometer transducer, such as a thermistor material. To ensure thermal isolation of the thermometer transducer from the readout substrate, the absorbing film is typically suspended above the readout substrate by anchor posts and thermally isolated from the readout substrate by holding arms. These anchor posts and holding arms also typically have an electrical function by connecting the absorbing film to readout circuitry located on the substrate. The absorbing film includes an absorber, e.g., a thin metal film, designed to absorb the electromagnetic radiation to be detected, which is thermally coupled to the thermometer transducer.

[0003] FIG. 1 is a perspective view of an exemplary thermal detector 1, according to one example in the prior art, designed to absorb infrared radiation, in this case within the long-wave infrared (LWIR) spectral band whose central wavelengths are comprised between approximately 8 μm and 12 μm.

[0004] The thermal detector 1 has an absorbent membrane 20 suspended above a readout substrate 10 by anchor posts 2 and insulated from the readout substrate 10 by holding and insulating arms 3. These anchor posts 2 and insulating arms 3 also have an electrical function by electrically connecting the absorbent membrane 20 to readout circuitry located on the readout substrate 10.

[0005] The film 20 includes an absorber 30, here designed to absorb the electromagnetic radiation to be detected, and a thermometer transducer in thermal contact with the absorber. The thermometer transducer can be a material with an electrical resistance that changes as it heats up (a thermistor). This can be amorphous silicon or vanadium oxide, among others. The absorbing film 20 is vertically spaced from the reflector 12 by a distance determined to form a quarter-wave interference cavity that optimizes the absorption of the electromagnetic radiation to be detected by the absorbing film 20. Such an absorber is therefore commonly referred to as a Salisbury absorber.

[0006] Document WO2020 / 084242A1 describes two structural configurations of absorbent membranes, which are similar to the Salisbury absorber in FIG. 1, i.e., λ c / 4n eq thin film absorbers spaced at a distance h equal to λ c is the total spectral band of detection, Δλ tot (in this case, 8-14 μm) is the central wavelength, and n eq is the equivalent refractive index of the medium associated with the quarter-wave cavity. Absorbers typically have a surface resistance close to the free-space impedance Z0 = 377 Ω.

[0007] In the first configuration, the polarized electrodes are polarized in the spectral band of detection Δλ tot They therefore act as absorbers of optical radiation within the spectral band Δλ of detection, if present in the quarter-wave cavity. tot (8~14μm) central wavelength λ c1 The reflector is vertically spaced a distance away from the reflector such that absorption is optimal for the reflector (in this case, approximately 11 μm).

[0008] In the second configuration, the polarized electrodes do not act as absorbers. In addition, a thin-film absorber is placed on the thermometer transducer perpendicular to the lateral spacing between the two polarized electrodes. In this way, the absorber does not vertically cover the polarized electrodes. This therefore reduces the spectral band of detection Δλ if material is present in the quarter-wave cavity. totThe central wavelength λ c1 The reflector is spaced perpendicularly from the reflector at a distance such that absorption is optimum for

[0009] However, while maintaining a uniformly high absorption (e.g., at least 70% across the entire spectral band of detection), the spectral band of detection Δλ tot However, the absorption spectrum of such an absorber extends beyond the wavelength λ c / 2n eq is limited by the presence of an antiresonance at Δλ, thus restricting absorption to low wavelengths and limiting the detection spectral band tot It is known that it is not possible to expand

[0010] It should be noted that US Patent Application Publication No. 2010 / 0148067 describes another configuration of an absorbing film, in which a first absorber is formed by polarized electrodes and placed above the thermometer transducer, which has an interdigitated comb-like shape and absorbs light in a spectral band Δλ centered at a wavelength of 10 μm. tot The reflector is spaced apart to form a quarter wave cavity that optimizes absorption within the reflector.

[0011] The absorbing film is placed below the absorber and absorbs the same spectral bands Δλ that would not have been absorbed by the upper absorber. tot The objective here is to improve the absorbance of the film, but without broadening the spectral band of detection. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] WO2020 / 084242A1 [Patent Document 2] U.S. Patent Application Publication No. 2010 / 0148067 Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to at least partially overcome the drawbacks of the prior art, and more particularly to propose a thermal detector having a broadband absorption spectrum while maintaining a uniformly high absorption rate over the entire spectral band of detection. [Means for solving the problem]

[0014] To achieve this, the object of the present invention is to tot a thermal detector of electromagnetic radiation in a readout substrate having a readout circuit and a reflector designed to reflect electromagnetic radiation; an absorbent membrane suspended above and thermally insulated from the readout substrate, the absorbent membrane having a thermometer transducer electrically connected to a readout circuit; It is thermally coupled to the thermometer transducer and has a wavelength λ c1 The spectral band Δλ is centered at tot is designed to absorb electromagnetic radiation within the spectral subband Δλ1 of wavelength λ c1 λ to form the first quarter-wave cavity C1 for c1 / 4n eq1 and is spaced from the reflector by a distance h1 equal to n eq1 a first thin film absorber with a total surface area S1, where S1 is the refractive index of the medium associated with the first quarter-wave cavity C1; at least one second thin film absorber with a total surface area S2, thermally coupled to the thermometer transducer, disposed on the absorbent membrane so as not to be covered by the first absorber; and a resorbable membrane having It has.

[0015] According to the present invention, the second absorber has a wavelength λ c2 The spectral band Δλ is centered at tot is designed to absorb electromagnetic radiation within the spectral subband Δλ2 of wavelength λc2 to form a second quarter-wave cavity C2 for λ c2 / 4n eq2 and spaced from the reflector by a distance h2 equal to n eq2 is the refractive index of the medium associated with the second quarter-wave cavity C2, and the spectral subband Δλ2 is c1 / 2, with a wavelength λ equal to within ±2 μm c2 Centered on.

[0016] The first and second absorbent bodies also have a total surface area such that the surface area ratio S2 / S1 is comprised between 0.5 and 3.

[0017] Some preferred but non-limiting aspects of this thermal detector are as follows:

[0018] The first absorber may be mounted on a thermometer transducer.

[0019] The second absorber may extend into the absorbent membrane without being covered by the thermometer transducer.

[0020] The second absorber can be formed, on the one hand, by polarized tracks on the holding arms that ensure support and thermal insulation of the absorbent membrane, and, on the other hand, by portions of a metal layer that form polarized electrodes that are in contact with the thermometer transducer.

[0021] The metal layer may extend planarly into the retaining arms and into the absorbent membrane.

[0022] The thermal detector detects the wavelength λ c3 The spectral band Δλ is centered at tot designed to absorb electromagnetic radiation within the spectral subband Δλ3 of wavelength λ c3 To form a quarter-wave cavity C3 for λ c3 / 4n eq3 and spaced from the reflector by a distance h3 equal to n eq3 is the refractive index of the medium associated with the quarter-wave cavity C3, and the wavelength λ c3is the wavelength λ c1 and λ c2 and a third absorber located between the first and second absorbers.

[0023] The distance h3 can be equal to the distance h2, and the third absorber is covered by the thermometer transducer.

[0024] The thermal detector detects the wavelength λ c4 The spectral band Δλ is centered at tot designed to absorb electromagnetic radiation within the spectral subband Δλ4 of wavelength λ c4 To form a quarter-wave cavity C4 for λ c4 / 4n eq4 and spaced from the reflector by a distance h4 equal to n eq4 is the refractive index of the medium associated with the quarter-wave cavity C4. The absorber of the quarter-wave cavity C4 may be a flat portion of an absorbing film that forms a step with respect to the main plane on which extends a metal layer that forms the polarization track arranged on the holding arm and the polarization electrode that contacts the thermometer transducer.

[0025] Spectral band of detection Δλ tot can include the spectral band LWIR, which ranges from 8 to 12 μm.

[0026] Thermal detection is performed in the spectral band Δλ tot It may have an absorption rate throughout at least equal to 80%.

[0027] Other aspects, objects, advantages and features of the present invention will become more apparent on 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: [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic, partial perspective view of an example of a thermal detector according to the prior art, as previously described; FIG. [Figure 2A] 1 is a partial schematic cross-sectional view of a thermal detector according to one embodiment; [Figure 2B] FIG. 2B is a top view of the thermal detector shown in FIG. 2A. [Figure 3A] FIG. 2 shows a schematic diagram of two Salisbury absorbers and a reflector of a thermal detector according to an embodiment. [Figure 3B] 3B shows an example of the total absorption spectrum and the absorption spectrum of the absorber of the thermal detector shown in FIG. 3A with a surface area ratio S2 / S1 equal to 1. FIG. [Figure 4A] 3B shows an example of the total absorption spectrum αtot(λ) and the absorption spectra α1(λ) and α2(λ) of the absorbers of the thermal detector shown in FIG. 3A with a surface area ratio S2 / S1 equal to 0.5. [Figure 4B] 3B shows an example of the total absorption spectrum αtot(λ) and the absorption spectra α1(λ) and α2(λ) of the absorbers of the thermal detector shown in FIG. 3A with a surface area ratio S2 / S1 equal to 2. [Figure 5A] FIG. 10 shows an example of the total absorption spectrum αtot(λ) of a thermal detector as a function of the surface area ratio S2 / S1 of the absorber. [Figure 5B] 5B shows several total absorption spectra αtot(λ) of the thermal detector for different values ​​of the surface area ratio S2 / S1 of the absorber from the example shown in FIG. 5A. [Figure 6A] 1 is a partial schematic cross-sectional view of a thermal detector according to one embodiment; [Figure 6B] 6B is another partial schematic cross-sectional view of the thermal detector shown in FIG. 6A. [Figure 6C] FIG. 6B is a top view of the thermal detector shown in FIG. 6A. [Figure 7A] 1 is a partial schematic cross-sectional view of a thermal detector according to one embodiment; [Figure 7B] FIG. 7B is a top view of the thermal detector shown in FIG. 7A. DETAILED DESCRIPTION OF THE INVENTION

[0029] In the figures, and in the remainder of the description, the same reference numerals represent the same or similar elements. Additionally, various elements have not been drawn to scale to ensure that the figures are as clear as possible. Also, different embodiments and variations are not mutually exclusive and can be combined together. Unless otherwise indicated, the terms "substantially," "about," and "on the order of" mean within a margin of 10%, preferably within a margin of 5%. Also, terms such as "included between" mean that the boundary is included unless otherwise stated.

[0030] The present invention provides a wide spectral band of detection, Δλ tot For thermal detectors of electromagnetic radiation, for example infrared or terahertz, in the spectral band Δλ tot The absorption is uniformly high throughout the spectrum, i.e., the absorption spectrum α tot (λ) is the spectral band Δλ tot For example, the spectral band of detection Δλ has a value at least equal to a predetermined threshold value throughout the entire spectrum. tot covers at least the LWIR range (8-12 μm), especially at shorter wavelengths.

[0031] The thermal detector may be part of a matrix of detectors in a detection device, the thermal detectors being identical and arranged periodically, each having an absorbing film suspended above the same readout substrate.

[0032] The absorbing film has at least two Salisbury absorbers thermally coupled to the same thermometer transducer (so that heat from the absorbers is transferred to the transducer) and defines at least two quarter-wave cavities with the same reflector on the readout substrate, at least one of the quarter-wave cavities having a resonant wavelength equal to plus or minus 2 μm of the antiresonant wavelength of another quarter-wave cavity.

[0033] In other words, as will be described in more detail below, the absorbing film is such that the first quarter-wave cavity C1 has a resonant wavelength λ c1(the center wavelength of the absorption spectrum band Δλ1 of the first absorber). Therefore, the first absorber is designed to optimize the absorption of the first absorber at λ c1 / 4n eq1 is spaced from the reflector at a vertical distance h1 equal to n eq1 is the equivalent refractive index of the media associated with the quarter-wave cavity C1, i.e., the media arranged perpendicular to the first absorber and reflector, and the media of the absorbing film arranged perpendicularly on the first absorber.

[0034] The absorbing film also has a resonant wavelength λ c2 (the center wavelength of the absorption band Δλ2 of the second absorber). Therefore, the second absorber is designed to optimize the absorption of the second absorber at λ c2 / 4n eq2 is spaced from the reflector at a vertical distance h2 equal to n eq2 is the effective refractive index of the medium associated with the quarter-wave cavity C2. The distance h2 and / or the refractive index n eq2 is the resonant wavelength λ c2 is the anti-resonance of the quarter-wave cavity C1, i.e., λ c1 / 2 within plus or minus 2 μm, i.e., λc2 = λc1 / 2 ± 2 μm, or λ c1 Thus, the spectral band of detection Δλ of the thermal detector is selected so that λc2 is λc1 / 2-2 μm≦λc2≦λc1 / 2+2 μm. tot is therefore broad insofar as it extends over at least two absorption spectral bands Δλ1 and Δλ2.

[0035] In addition, the absorption spectrum α of the thermal detector tot (λ) is the detected spectral band Δλ tot The surface area ratio S between the absorbers should be set to a uniformly high value throughout i / S j is included between 0.5 and 3, where the surface area S icorresponds to the total surface area of ​​the absorber of rank i, whose resonant wavelength is substantially equal to the antiresonant wavelength of the absorber of rank j (±2 μm). Therefore, the total absorption spectrum α tot The contributions to (λ) are balanced, which results in a total absorption of the detected spectral band Δλ tot The surface area S of the absorber is defined as the total surface area of ​​the quarter-wave cavity in question, i.e., located at a certain distance h from the reflector.

[0036] Figure 2A is a partial schematic diagram of a thermal detector 1 for electromagnetic radiation, in this case infrared radiation, in cross section along section line AA (see Figure 2B), according to one embodiment. Figure 2B is a partial schematic top view of the thermal detector 1 shown in Figure 2A.

[0037] A three-dimensional direct reference frame XYZ is defined here, and for the remainder of the description, where the plane XY is substantially parallel to the plane of the readout substrate 10 of the thermal detector 1 and the axis Z is oriented substantially perpendicular to the plane XY of the readout substrate 10 in the direction of the absorbent film 20. Also, the terms "lower" and "upper" are understood to refer to locations that increase when moving away from the readout substrate 10 in the +Z direction.

[0038] The readout substrate 10 consists of a support substrate 11 containing readout circuitry (not shown) designed to control and readout the thermal detector 1. The readout circuitry may be in the form of a CMOS integrated circuit. It therefore has conductive portions that are substantially planar, flush with the top surface of the readout substrate 10. The conductive portions and conductive vias may be made of copper, aluminum and / or tungsten, among others, for example by a damascene process in which trenches etched in an intermetal insulating layer are filled.

[0039] The thermal detector 1 has a reflector 12, which rests on or in the readout substrate 10. It is designed to reflect the electromagnetic radiation to be detected towards the absorbing film 20 and is preferably made of at least one metallic material. It can be covered by a protective layer made of a material that is substantially inert to the etching solution subsequently used to remove the sacrificial layer used to manufacture the suspended film 20 as well as the encapsulation structure (which defines the vacuum cavity in which the absorbing film 20 is located). The reflector 12 extends in the plane XY below the absorbing film 20, and in particular below the absorber arranged therein.

[0040] The thermal detector 1 has an absorbing membrane 20 that is suspended above a readout substrate 10 by anchor posts 2 and insulated from the readout substrate 10 by holding and insulating arms 3. The anchor posts 2 and holding arms 3 also provide electrical connections to the readout circuitry contained in the readout substrate 10. The holding arms 3 may be formed by a stack of a lower insulating layer 21 (e.g. Al2O3 or amorphous silicon), a polarized conductor track 32 (e.g. TiN or NiCr), and an upper insulating layer 22 (e.g. Al2O3 or amorphous silicon).

[0041] The absorbent film 20 has a thermometer transducer 23, in the present case formed by a thermistor layer, i.e. a layer made of a material whose electrical resistance changes depending on the heating of its temperature, polarized electrodes, and at least two absorbers 31, 32 thermally coupled to the same thermometer transducer 23.

[0042] In this example, the absorbing film 20 comprises a lower insulating layer 21 made of a dielectric material such as aluminum oxide, oxide and / or silicon nitride, or of an unintentionally doped semiconductor material such as amorphous silicon, which may have a thickness comprised for example between 5 nm and 100 nm, preferably between 15 nm and 50 nm.

[0043] Polarization electrodes rest on the lower insulating layer 21. They are made of a conductive material, in this case, in particular a metallic material such as TiN or NiCr, and have a thickness of, for example, between 5 and 15 nm, preferably between 6 and 10 nm. As will be explained below, these polarization electrodes form the so-called lower thin-film absorber 32 here. However, the lower absorber may alternatively be separate from the polarization electrodes. The material and thickness of the lower absorber 32 are preferably selected so that its surface resistance is substantially equal to the impedance of free space.

[0044] The lower absorber 32 is thus formed by two spatially distinct portions 32.1 and 32.2, which extend from the holding arm 3 to the edge of the thermometer transducer 23 so as to be able to electrically polarize the thermometer transducer 23. In this example, each portion of the lower absorber 32 extends in a C-shape so as to cover most of the absorbent film 20. On the other hand, in the thermometer transducer 23, the two portions 32.1 and 32.2 are spaced apart laterally in the XY plane sufficiently so as not to be perpendicular to the upper absorber 31. The surface area S2 of the lower absorber 32 corresponds to the sum of the surface areas of the two individual portions 32.1 and 32.2. In this case, each portion of the lower absorber 32 extends continuously with a constant thickness. Alternatively, it may extend discontinuously and have a non-constant thickness.

[0045] The lower absorber 32 is positioned at a substantially constant distance h2 from the reflector 12, and therefore at a resonant wavelength λ c2 form a quarter-wave cavity C2 where h2=λ c2 / 4n eq2 Wavelength λ c2 is the spectral band Δλ tot is the center wavelength of the spectral subband Δλ2 of eq2 is the equivalent refractive index of the medium associated with the quarter-wave cavity C2, i.e., the medium located between the lower absorber 32 and the reflector 12, vertically above the lower absorber 32, and the medium located on and vertically above the lower absorber 32. As will be explained in more detail below, the distance h2 and / or the refractive index neq2 is the wavelength λ c2 is the anti-resonant wavelength λ of the quarter-wave cavity C1 c1 The radii are chosen to be equal to within plus or minus 2 μm of / 2.

[0046] The thermometer transducer 23 in this case extends over and in contact with the polarizing electrodes and the lower insulating layer 21. It is a thermistor material, for example, with a thickness of the order of a few dozen to a few hundred nanometers. It can be a material containing vanadium or titanium oxide or amorphous silicon. Alternatively, it can be a diode (pn or pin junction) or a metal oxide semiconductor field effect transistor (MOSFET), among others.

[0047] An upper protective layer 24 covers the thermometer transducer 23 only on its top surface in this case, but it can completely cover the thermometer transducer 23 to protect it from possible contamination or damage during the manufacturing method steps. It can be made of an electrically insulating material, for example a dielectric material such as silicon oxide, nitride or oxynitride, or even aluminum oxide, among others, and has a thickness of a few dozen nanometers.

[0048] The absorbing film 20 has a second absorber 31, the so-called upper absorber, formed by a thin film of at least one material designed to absorb the electromagnetic radiation to be detected, for example made of a metallic material such as TiN or NiCr, among others, with a thickness of, for example, between 5 and 15 nm, preferably between 6 and 10 nm. The upper absorber 31 is thermally coupled to the thermometer transducer 23. It rests here on an upper protective layer 24 and does not extend in the opposite direction (vertically) to the lower absorber 32, so as to prevent impairing the absorption of the electromagnetic radiation by one or the other of the absorbers.

[0049] The material and thickness of the upper absorber 31 are preferably selected so that its surface resistance is substantially equal to the impedance of free space. In this case, it extends continuously with a constant thickness. Alternatively, it can extend discontinuously and have a non-constant thickness. S1 is the total surface area of ​​the upper absorber 31.

[0050] The upper absorber 31 is positioned at a substantially constant distance h1 from the reflector 12, and therefore at a resonant wavelength λ c1 form a quarter-wave cavity C1 where h1=λ c1 / 4n eq1 Wavelength λ c1 is the spectral band Δλ tot is the center wavelength of the spectral subband Δλ1 of eq1 is the equivalent refractive index of the medium associated with the quarter-wave cavity C1, i.e., the medium located between the upper absorber 31 and the reflector 12, and vertically above the upper absorber 31, as well as the medium located on and vertically above the upper absorber 31.

[0051] According to the present invention, the absorbing film 20 is therefore adapted to detect the spectral band Δλ tot The cavity C2 has at least two Salisbury absorbers 31, 32 designed to absorb electromagnetic radiation within a resonant wavelength λ associated with the quarter-wave cavity C2. c2 is the anti-resonant wavelength λ associated with the quarter-wave cavity C1 c1 / 2 to within ±2 μm. This configuration can be adjusted by adjusting one and / or the other of the distances h1 and h2, or by the choice of material and thickness, to obtain the equivalent refractive index n eq1 and n eq2 can be obtained by adjusting one and / or the other.

[0052] Therefore, the total absorption spectrum α of the thermal detector 1 tot (λ) corresponds to the sum of the absorption spectrum α1(λ) of the upper absorber 31 and the absorption spectrum α2(λ) of the lower absorber 32. totis no longer limited by the anti-resonance of the quarter-wave cavity C1, nor does it appear to be limited by the anti-resonance of the quarter-wave cavity C2 (as will be explained in more detail below with reference to FIG. 3B).

[0053] Also, the surface area ratio S2 / S1 is comprised between 0.5 and 3, preferably between 0.8 and 2, and preferably approximately equal to 1. Thus, the total absorption spectrum α of the thermal detector 1 tot The contribution of each absorber 31, 32 to (λ) is balanced, resulting in a spectral band Δλ tot at least a predetermined threshold α tot,th A uniformly high absorption value α equal to tot is brought about.

[0054] It should be noted that the lower absorber 32, which in this case also forms a polarized electrode, has a much larger total surface area than the prior art where the electrodes are narrow tracks and do not form a Salisbury absorber.

[0055] Total absorption spectrum α of thermal detector 1 tot To explain the contribution of absorbers 31, 32 to (λ), we now consider two absorbers 31, 32 and a reflector 12 as shown schematically in Figure 3A. Figures 3B, 4A and 4B show the total absorption spectrum α of the absorbing film 20. tot (λ) and examples of these α1(λ) and α2(λ) of the upper absorber 31 and the lower absorber 32 are shown, where the surface area ratio S2 / S1 is approximately equal to 1 (FIG. 3B), approximately equal to 0.5 (FIG. 4A), and approximately equal to 2 (FIG. 4B).

[0056] In this example, the lower absorber 32 is made of TiN with a thickness of 8 nm and extends in the plane XY as a square ring. It is spaced vertically from the reflector 12 by a distance h2, which in this case is equal to 1.5 μm. Furthermore, the upper absorber 31 is made of TiN with a thickness of 8 nm and extends in the plane XY as a square. Its dimension is equal to the empty inner space of the lower absorber 32 in this case. It is spaced vertically from the reflector 12 by a distance h1 = h2 + δ, which in this case is equal to 2.5 μm. Furthermore, the pixel pitch is equal to 12 μm in this case and is determined by the formula ff = (S2 + S1) / p 2 The fill factor ff defined by is equal to 80%.

[0057] The absorption spectrum is now obtained by numerically solving Maxwell's equations using finite elements.

[0058] The absorption spectrum α1(λ) of the upper absorber 31 has a resonant wavelength λ, which here is approximately equal to 13 μm. c1 and decreases sharply at the anti-resonance wavelength of approximately 5 μm. Furthermore, the absorption spectrum α2(λ) of the lower absorber 32 decreases sharply at the resonant wavelength λ, which is equal to approximately 6 μm here. c2 The absorption spectrum α tot (λ) no longer appears to decrease sharply at the antiresonant wavelengths of 5 μm (approximately 60% absorption) and 3 μm (approximately 40% absorption).

[0059] Also, the contribution of each absorber 31, 32 is homogeneous here since the surface area ratio S2 / S1 is approximately equal to 1, so the total absorption spectrum α tot (λ) is the detected spectral band Δλ tot Therefore, if the absorption threshold is assumed to be equal to 40%, the spectral band of detection Δλ totranges from 3 μm to more than 20 μm. If this is assumed to be 60%, this ranges from 5 μm to more than 20 μm. If this is assumed to be 80%, this ranges from 6 to 15 μm. Therefore, the spectral band of detection Δλ tot is considerably broadened, and the total absorption spectrum α tot (λ) is uniformly high, i.e., the spectral band Δλ tot At least equal to the threshold throughout.

[0060] Here, the maximum lateral dimension of the absorbers 31, 32 is the spectral band Δλ tot It should be noted that it is advantageous to set the wavelength of the spectrum at or below the central wavelength of the spectral band Δλ between 6 and 15 μm (80% absorption threshold). tot is approximately equal to 11 μm. Here, the upper absorber 31 is a square with sides of 7.6 μm, and the lower absorber 32 is a square ring with sides of 10.7 μm. In addition, the lateral dimensions of the absorbers are less than the central wavelength of 11 μm.

[0061] This configuration then appears to maximize the efficiency of optical collection of incident electromagnetic radiation. Indeed, the upper absorber 31, although its relative surface area is 40%, absorbs up to 65% around its resonant wavelength of 13 μm. Similarly, the lower absorber 32, although its relative surface area is also 40%, absorbs up to 60% around its resonant wavelength of 5 μm. The combination of the two absorbers 31, 32, which cover a total relative surface area of ​​80% of the surface of the detection pixel, makes it possible to absorb more than 80% of the incident radiation between 6 and 15 μm.

[0062] The total absorption spectrum α of the thermal detector 1 is calculated by adjusting the contribution of each absorption spectrum α(λ) and α(λ) via the surface area ratio S / S. tot It is possible to modify (λ).

[0063] When the surface area ratio S2 / S1 is equal to 0.5 (see FIG. 4A), the contribution of the lower absorbent body 32 is now reduced in favor of the upper absorbent body 31. When the surface area ratio S2 / S1 is equal to 2 (see FIG. 4B), the contribution of the lower absorbent body 32 increases to the detriment of the upper absorbent body 31.

[0064] Thus, when the absorption threshold is equal to 60%, S2 / S1 = 0.5 (Fig. 4A), and the maximum absorption is 90% around 12 μm, the absorption spectral band Δλ tot ranges from 6 μm to more than 20 μm. On the other hand, when S2 / S1 = 2 (Figure 4B), and the maximum absorption is 90% around 7-8 μm, this ranges from 4 μm to 20 μm.

[0065] FIG. 5 shows an exemplary total absorption spectrum α as a function of the surface area ratio S2 / S1 for the configuration shown in FIG. 3A. tot 5B shows the total absorption spectrum α for S2 / S1=0.5, S2 / S1=3, and for very small S2 / S1 (S2 / S1<<1, where the upper absorber 31 fills the entire available surface area), and for very large S2 / S1 (S2 / S1>>1, where the lower absorber 32 fills the entire available surface area). tot (λ) is shown.

[0066] Total absorption spectrum α with very small S2 / S1 tot In (λ), the spectrum peaks at the antiresonant wavelength of the quarter-wave cavity C1, i.e., approximately 5 μm. Similarly, the total absorption spectrum α, where S2 / S1 is very large, tot In (λ), the spectrum peaks at the antiresonant wavelength of the quarter-wave cavity C2, i.e., approximately 3 μm. The total absorption spectrum α for S2 / S1 = 0.5 and S2 / S1 = 3 tot These absorption limitations are not observed in (λ).

[0067] Figures 6A and 6B are partial schematic diagrams of a thermal detector 1 for electromagnetic radiation according to one embodiment, in cross section along section lines AA and BB (see Figure 6C), respectively. Figure 6C is a top view of the thermal detector 1 shown in Figures 6A and 6B.

[0068] In this example, the absorbing film 20 has the same thermometer transducer 23 thermally coupled to more than two absorbers, in this case three absorbers 31, 32, 33 forming three separate quarter-wave cavities C1, C2, C3 for the absorption spectral bands.

[0069] The absorbing film 20 here comprises a lower insulating layer 21, two spatially distinct portions of a thin metal film in the plane XY forming the polarizing electrodes and the second and third absorbers 32, 33, an upper insulating layer 22, a thermometer transducer 23 (in this case a layer of thermistor material) resting on the upper insulating layer and passing through it at an opening 22a to contact the metal layer, an upper protective layer 24 covering the thermometer transducer 23, and a thin metal film resting on the thermometer transducer 23 forming the first absorber 31 (upper absorber).

[0070] The upper absorber 31 is positioned above the thermometer transducer 23 at a distance h1 from the reflector 12. The quarter-wave cavity C1 absorbs light at wavelength λ in the spectral band Δλ. c1 This allows optimizing absorption by the upper absorber 31 in the thermometer transducer 23. The medium includes in particular the upper protective layer 24, the thermistor material 23 and the two insulating layers 22, 21. As shown in Figure 6C, the upper absorber 31 only extends over part of the surface of the thermometer transducer 23, in this case over approximately half of its surface.

[0071] Furthermore, the metal layer formed by the two polarized electrode portions forms a second absorber 32 (quarter-wave cavity C2) spaced a distance h2 from the reflector 12. In this quarter-wave cavity C2, the second absorber 32 extends into the absorbing film 20 without being covered by the thermometer transducer 23. The absorption by this second absorber 32 is at a wavelength λc2 The medium associated with this quarter-wave cavity C2 here comprises in particular two insulating layers 21, 22.

[0072] In the third quarter-wave cavity C3, the metal layer extends over the absorbing film 20 and is covered by the thermometer transducer 23 (but not by the first absorber). More specifically, the two portions 33.1 and 33.2 of the metal layer covered by the thermometer transducer 23 form the third absorber 33, which is spaced the same distance h2 from the reflector 12 as the second absorber 32. The absorption by this third absorber 33 is at wavelength λ c3 The medium associated with this quarter-wave cavity C3 here includes in particular an upper protective layer 24, a thermistor transducer 23 and two insulating layers 22, 21.

[0073] Thus, three quarter-wave cavities C1, C2, C3 have heights h1 and h2 (in this case the distance h3 of the third absorber is equal to h2) and equivalent refractive indices n eq1 , n eq2 and n eq3 Regarding the absorption value α above the reference value, tot Wide detection spectral band Δλ while maintaining tot Thus, quarter-wave cavity C2 can be designed to absorb optimally at the antiresonance of quarter-wave cavity C1. Quarter-wave cavity C3 can be designed to absorb within a spectral band Δλ3 comprised between Δλ1 and Δλ2, for example, by adjusting the thickness of such a layer of absorbing film 20 disposed in or on quarter-wave cavity C3.

[0074] Figure 7A is a partial schematic cross-sectional view of a thermal detector 1 for electromagnetic radiation according to an embodiment, taken along section line AA (see Figure 7B), and Figure 7B is a top view of the thermal detector 1 shown in Figure 7A.

[0075] In this example, the absorbing film 20 has the same thermometer transducer 23 thermally coupled to more than two absorbers, in this case five absorbers 31, 32, 33, 34 and 35 forming five separate quarter-wave cavities for the absorption spectral bands.

[0076] The absorbing film 20 now comprises a lower insulating layer 21, a thin metal film in a plurality of spatially distinct portions in the plane XY forming polarizing electrodes and a plurality of different absorbers, an upper insulating layer 22, and a thermometer transducer 23 (here a layer of thermistor material) resting on the upper insulating layer and passing through it at opening 22a to contact the metal layer. An upper protective layer 24 covers the thermometer transducer 23.

[0077] Different portions of the metal film form different absorbers 31 to 35 to define the quarter-wave cavities. In this example, there is no upper absorber resting on the thermometer transducer 23, although alternatively there could be such an upper absorber (in which case there would be no absorber covered by the thermometer transducer 23).

[0078] The two central parts form a first absorber 31 spaced a distance h1 from the reflector 12. They are covered by the thermometer transducer 23 and have a resonant wavelength λ 1 in the spectral band Δλ 1 . c1 defines a quarter-wave cavity C1 with a refractive index n eq1 The medium includes in particular a thermometer transducer 23 and two insulating layers 21, 22.

[0079] The side forms another absorber 35, spaced the same distance h1 from the reflector 12, which is not covered by the thermometer transducer 23 and which has a resonant wavelength λ in the spectral band Δλ. c5 defines a quarter wave cavity C5 with a refractive index n eq5 The medium comprises in particular two insulating layers 21,22.

[0080] The three other sides form different absorbers 32, 33, 34, which are spaced apart from each other and from the reflector 12 by distances h2, h3 and h4 different from the value h1. They are not covered by the thermometer transducer 23, and they form a quarter-wave cavity. c2 , C3 and C4, whose resonant wavelengths are λ c2 , λ c3 , and λ c4 The refractive index is n eq2 , n eq3 and n eq4 The medium essentially comprises two insulating layers.

[0081] In addition, the absorbing film has different levels at which the absorbers 32, 33, 34 are arranged. These therefore have flat portions at which the absorbers 32, 33, 34 are spaced apart from the reflector 12 by respective distances h2, h3 and h4, connected to a main flat portion at which the thermometer transducer 23 is arranged by a vertical (as shown) or inclined connecting portion. The flat portions at which the absorbers 32, 33, 34 are arranged therefore form steps of the absorbing film 20 relative to the main flat portion.

[0082] Thus, the absorbing film 20 has heights h1 to h5 and equivalent refractive index n eq1 From eq 5, the absorption value α above the reference value tot Wide detection spectral band Δλ while maintaining tot Multiple quarter-wave cavities can be designed to absorb optimally at the antiresonances of other quarter-wave cavities, which can also be designed to absorb in spectral bands that fall between those of the other quarter-wave cavities.

[0083] While specific embodiments have been described above, various modifications and variations will become apparent to those skilled in the art. [Explanation of symbols]

[0084] 1. Heat detector 2 anchor posts 3 Insulated Arm 10 Readout board 11 Support substrate 12 Reflector 20 Absorbable membrane 21 Lower insulating layer 22 Upper insulating layer 23 Thermometer Transducer 24 Upper protective layer 31 First absorber 32 Second absorber 32.1 Part 32.2 Part 33 Third Absorber 33.1 Part 33.2 Part 34 Absorbent 35 Absorbent

Claims

1. Predetermined spectral band Δλ tot A thermal detector (1) configured to absorb electromagnetic radiation within a readout substrate (10) having a readout circuit and a reflector (12) configured to reflect said electromagnetic radiation; an absorbent membrane (20) suspended above and thermally insulated from said readout substrate (10), said membrane having a thermometer transducer (23) electrically connected to said readout circuitry; thermally coupled to the thermometer transducer (23); wavelength λ c1 The spectral band Δλ is centered at tot Spectral subbands Δλ 1 configured to absorb the electromagnetic radiation within the wavelength λ c1 First quarter-wave cavity for C 1 λ so as to form c1 / 4n eq1 A value h equal to 1 and n eq1 is the first quarter-wave cavity C 1 is the refractive index of the medium related to Total surface area S 1 A first thin film absorber (31) comprising: thermally coupled to the thermometer transducer (23); It is arranged on the absorbent membrane (20) so as not to be covered by the first thin film absorbent body (31), Total surface area S 2 At least one second thin film absorber (32) comprising: an absorbent membrane (20) having A thermal detector (1) having The second thin film absorber (32) has a wavelength λ c2 The spectral band Δλ is centered at tot Spectral subbands Δλ 2 configured to absorb the electromagnetic radiation within the wavelength λ c2 A second quarter-wave cavity for C 2 λ so as to form c2 / 4n eq2 A value h equal to 2 and n eq2 is the second quarter-wave cavity C 2 is the refractive index of the medium associated with said spectral subband Δλ 2 is λ c1 The wavelength λ is equal to within ±2 μm of c2 To be centered on The first and second thin film absorbers (31, 32) have a surface area ratio S 2 / S 1 having a total surface area such that: and the second thin film absorber (32) extends into the absorbent film (20) without being covered by the thermometer transducer (23). Heat detector (1).

2. 2. The thermal detector (1) of claim 1, wherein the first thin film absorber (31) rests on the thermometer transducer (23).

3. 2. A thermal detector (1) according to claim 1, wherein the second thin-film absorber (32) is formed by portions (32.1, 32.2) of a metal layer which, on the one hand, form polarized tracks on the holding arms (3) which ensure support and thermal insulation of the absorbent membrane (20) and, on the other hand, form polarized electrodes which are in contact with the thermometer transducer (23).

4. 4. The thermal detector (1) according to claim 3, wherein said metal layer extends planarly into said holding arm (3) and into said absorbent membrane (20).

5. wavelength λ c3 The spectral band Δλ is centered at tot Spectral subbands Δλ 3 configured to absorb said electromagnetic radiation within a wavelength λ c3 Quarter-wave cavity for C 3 λ so as to form c3 / 4n eq3 A value h equal to 3 and n eq3 is the quarter-wave cavity C 3 is the refractive index of the medium related to said wavelength λ c3 is the wavelength λ c1 and λ c2 2. The thermal detector (1) of claim 1, further comprising a third absorber (33) located between said first and second absorbers.

6. distance h 3 is the distance h 2 and the third absorber (33) is covered by the thermometer transducer (23).

7. wavelength λ c4 The spectral band Δλ is centered at tot Spectral subbands Δλ 4 configured to absorb said electromagnetic radiation within a wavelength λ c4 Quarter-wave cavity for C 4 λ so as to form c4 / 4n eq4 A value h equal to 4 and n eq4 is the quarter-wave cavity C 4 the quarter-wave cavity C having at least one absorber, 4 2. The thermal detector (1) according to claim 1, wherein the absorber is in a flat part of the absorbing film (20) that forms a step with respect to a main plane in which extends a metal layer that forms a polarizing electrode that is in contact with the polarizing track arranged on the holding arm (3) and the thermometer transducer (23).

8. Detection of the spectral band Δλ tot The thermal detector (1) according to claim 1, comprising the spectral band LWIR, which is in the range from 8 to 12 μm.

9. Detection of the spectral band Δλ tot 2. A thermal detector (1) according to claim 1, having an absorption rate at least equal to 80% throughout.

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