Wideband thermal detector with multiple quarter-wave cavities

Abstract

The invention relates to a broadband thermal detector with a plurality of quarter-wave cavities, having at least two absorbers (31, 32). The second absorber (32) is designed to absorb electromagnetic radiation in a spectral sub-band [delta] [lambda] 2 centered on wavelength [lambda] c2 of a predetermined spectral band [delta] [lambda] tot. Furthermore, the second absorber is spaced apart from the reflector (12) by a value h2 equal to [lambda] c2 / 4 neq2 so as to form with the reflector a quarter-wave cavity C2 of a wavelength [lambda] c2, the spectral sub-band [delta] [lambda] 2 being centered on the wavelength [lambda] c2 equal to [lambda] c1 / 2 (within + / -2 [mu] m). Furthermore, the first absorber (31) and the second absorber (32) have a total surface area such that a surface area ratio S2 / S1 is between 0.5 and 3.

Description

Technical Field

[0001] The field of the invention is a device for detecting electromagnetic radiation, such as infrared radiation or terahertz radiation, having at least one thermal detector having an absorbing film suspended above a readout substrate. The invention is particularly applicable in the field of infrared imaging, in the field of thermal imaging and in particular in the field of gas detection. Background Art

[0002] The device for detecting electromagnetic radiation may comprise a matrix of thermal detectors, each thermal detector having a film designed to absorb the electromagnetic radiation to be detected and containing a thermometer transducer (such as a thermistor material). In order to ensure that the thermometer transducer is thermally isolated from the readout substrate, the absorbing film is usually suspended above the readout substrate by anchoring posts and is thermally isolated from the readout substrate by retaining arms. These anchoring posts and retaining arms also have an electrical function by connecting the absorbing film to a readout circuit that is usually arranged in the substrate. The absorbing film has an absorber (for example a thin metal film) designed to absorb the electromagnetic radiation to be detected, which absorber is thermally coupled to the thermometer transducer.

[0003] Figure 1 is a perspective view of an exemplary thermal detector 1 according to an example in the prior art, in which case the thermal detector is designed to absorb infrared radiation in the Long-Wave Infrared (LWIR) spectral band, with a central wavelength between approximately 8 μm and 12 μm.

[0004] The thermal detector 1 has an absorbing film 20 which is suspended above the readout substrate 10 by anchoring posts 2 and which is thermally insulated from the readout substrate by holding thermally insulating arms 3. These anchoring posts 2 and thermally insulating arms 3 also have an electrical function by electrically connecting the absorbing film 20 to a readout circuit located in the readout substrate 10.

[0005] The membrane 20 has an absorber 30, which is designed here to absorb the electromagnetic radiation to be detected, and a thermometer transducer, which is in thermal contact with the absorber. The thermometer transducer can be a material whose resistance changes as it heats up (thermistor). The thermometer transducer can especially be amorphous silicon or vanadium oxide. The absorbing membrane 20 is vertically spaced apart from the reflector 12 by a distance determined to form a quarter-wave interference cavity, which optimizes the absorption of the electromagnetic radiation to be detected by the absorbing membrane 20. Therefore, this absorber is often called a Salisbury absorber.

[0006] Document WO2020 / 084242A1 describes two structural configurations of an absorbent film, the absorbent film comprising Figure 1 The Salisbury absorber in the similar Salisbury absorber, that is, located at a position equal to λ c / 4n eq The thin film absorber is at a distance h from the c is the total detected spectral band Δλ tot The central wavelength of the eq is the equivalent refractive index of the medium associated with the quarter-wave cavity. The surface resistance of the absorber is usually close to the free space impedance Z 0 =377Ω.

[0007] In the first configuration, the polarization electrode acts as a detection spectral band Δλ tot Therefore, the polarization electrode is vertically spaced apart from the reflector by a distance such that, taking into account the materials present in the quarter-wave cavity, the detection spectral band Δλ tot (8μm to 14μm) center wavelength λ c1 (about 11 μm in this case), absorption is optimal.

[0008] In the second configuration, the polarization electrodes do not act as absorbers. In addition, the thin film absorber is located on the thermometer transducer, perpendicular to the lateral spacing between the two polarization electrodes. In this way, the absorber does not vertically cover the polarization electrodes. Therefore, the polarization electrodes are vertically spaced apart from the reflector by a distance such that, taking into account the materials present in the quarter-wave cavity, the detection spectral band Δλ is tot The central wavelength λ c1 , absorption is optimal.

[0009] However, it is necessary to broaden the detection spectral band Δλ tot (especially at shorter wavelengths) while maintaining uniformly high absorptivity (e.g., at least 70% across the entire detection spectral band). However, it is known that the absorption spectrum of such absorbers is affected by the wavelength λ C / 2n eq The presence of antiresonance at λ limits the absorption to low wavelengths and makes the detection spectral band Δλ tot Cannot be widened.

[0010] It should be noted that document US2010 / 0148067A1 describes another configuration of an absorbing film, in which a first absorber is formed by polarized electrodes and is located above the thermometer transducer. This first absorber is shaped like a crossed comb and is spaced apart from the reflector to form a quarter-wave cavity that optimizes the spectral band Δλ centered around a wavelength of 10 μm. tot Absorption in.

[0011] The absorbing film has a second absorber which is located below the absorber and is designed to absorb the same spectral band Δλ totThe light radiation in the film is not absorbed by the upper absorber. The purpose here is to increase the absorbance of the film. However, the detection spectral band is not broadened. Summary of the invention

[0012] The object of the present invention is to at least partially overcome the disadvantages of the prior art, and more specifically, to provide a thermal detector having a broadband absorption spectrum while maintaining uniform high absorption over the entire detection spectral band.

[0013] To achieve this, the object of the present invention is a method for generating a spectral signal in a predetermined spectral band Δλ. tot A thermal detector for electromagnetic radiation in a reactor, the thermal detector having:

[0014] o a readout substrate having: a readout circuit; a reflector designed to reflect electromagnetic radiation;

[0015] o an absorbing film suspended above a readout substrate, the absorbing film being thermally isolated from the readout substrate, the absorbing film having a thermometer transducer electrically connected to a readout circuit, and the absorbing film having:

[0016] A first thin film absorber having a total surface area S 1 , the first thin film absorber is thermally coupled to the thermometer transducer, and the first thin film absorber is designed to absorb the spectral band Δλ tot The wavelength λ c1 The spectral subband Δλ is centered 1 The electromagnetic radiation in the first film absorber is spaced apart from the reflector by a distance equal to λ c1 / 4n eq1 The value of h 1 , thus forming a wavelength λ with the reflector c1 The first quarter-wave cavity C 1 , n eq1 is related to the first quarter-wave cavity C 1 the refractive index of the associated medium;

[0017] At least one second thin film absorber, the at least one second thin film absorber having a total surface area S 2 , at least one second thin film absorber is thermally coupled to the thermometer transducer, the at least one second thin film absorber being arranged in the absorber film so as not to be covered by the first absorber.

[0018] According to the present invention, the second absorber is designed to absorb the spectral band Δλ tot The wavelength λ c2 The spectral subband Δλ is centered 2 The electromagnetic radiation in the second absorber is spaced apart from the reflector by a distance equal to λ c2 / 4neq2 The value of h 2 , thus forming a wavelength λ with the reflector c2 The second quarter wave cavity C 2 , n eq2 is with the second quarter-wave cavity C 2 The refractive index of the associated medium, spectral subband Δλ 2 With wavelength λ c2 Centered at wavelength λ c2 Equal to λ c1 / 2 (within plus or minus 2μm).

[0019] Furthermore, the first absorber and the second absorber have a total surface area such that the surface area ratio S 2 / S 1 Between 0.5 and 3.

[0020] Certain preferred but non-limiting aspects of the thermal detector are as follows.

[0021] The first absorber may rest against the thermometer transducer.

[0022] The second absorber may extend into the absorber film without being covered by the thermometer transducer.

[0023] The second absorber is formed by a plurality of parts of a metal layer which forms on the one hand a polarization track at the holding arm, which ensures support and thermal insulation of the absorber film, and on the other hand a polarization electrode which is in contact with the thermometer transducer.

[0024] The metal layer can extend in a planar manner into the retaining arm and into the absorbent film.

[0025] The thermal detector may have a third absorber designed to absorb the spectral band Δλ tot The wavelength λ c3 The spectral subband Δλ is centered 3 The electromagnetic radiation in the third absorber is spaced apart from the reflector by a distance equal to λ c3 / 4n eq3 The value of h 3 , thus forming a wavelength λ with the reflector c3 The quarter wave cavity C 3 , n eq3 is with the quarter-wave cavity C 3 The refractive index of the associated medium, wavelength λ c3 Between wavelength λ c1 To wavelength λ c2 between.

[0026] Distance 3 can be equal to the distance h 2, the third absorber is covered by a thermometer transducer.

[0027] The thermal detector may have at least one absorber, the at least one absorber being designed to absorb in the spectral band Δλ tot The wavelength λ c4 The spectral subband Δλ is centered 4 The electromagnetic radiation in the at least one absorber is spaced from the reflector by a distance equal to λ c4 / 4n eq4 The value of h 4 , thus forming a wavelength λ with the reflector c4 The quarter wave cavity C 4 , n eq4 is with the quarter-wave cavity C 4 The refractive index of the associated medium. Quarter-wave cavity C 4 The absorber can be located on a flat portion of the absorber film, which forms a step relative to the main plane in which the metal layer extends to form a polarization track located in the retaining arm and a polarization electrode in contact with the thermometer transducer.

[0028] Detection spectral band Δλ tot The spectral band LWIR ranging from 8 μm to 12 μm may be included.

[0029] The thermal detector has a full detection spectral band Δλ tot The absorption on is at least equal to 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other aspects, objects, advantages and features of the present invention will become more apparent on reading the following detailed description of a preferred embodiment of the invention given as a non-limiting example and made with reference to the accompanying drawings, in which:

[0031] Already described Figure 1 is a schematic partial perspective view of a thermal detector according to an example of the prior art;

[0032] Figure 2A is a partial schematic cross-sectional view of a thermal detector according to one embodiment;

[0033] Figure 2B yes Figure 2A A top view of the thermal detector shown in ;

[0034] Figure 3A schematically illustrates two Salisbury absorbers and reflectors of a thermal detector according to one embodiment;

[0035] Figure 3B Shows Figure 3A An example of the total absorption spectrum of the thermal detector and the absorption spectrum of the absorber is shown in FIG. , where the surface area ratio S2 / S 1 is equal to 1;

[0036] Figure 4A Shows Figure 3A The total absorption spectrum of the thermal detector shown in α tot (λ) and the absorption spectrum of the absorber α 1 (λ) and α 2 (λ) example, where the surface area ratio S 2 / S 1 =0.5;

[0037] Figure 4B Shows Figure 3A The total absorption spectrum of the thermal detector shown in α tot (λ) and the absorption spectrum of the absorber α 1 (λ) and α 2 (λ) example, where the surface area ratio S 2 / S 1 is equal to 2;

[0038] Figure 5A shows the total absorption spectrum of the thermal detector α tot (λ) varies with the absorber surface area ratio S 2 / S 1 Examples of changes;

[0039] Figure 5B Shows the corresponding Figure 5A The surface area ratio S of the absorber for the example shown in 2 / S 1 Multiple total absorption spectra of the thermal detector for different values ​​of α tot (λ);

[0040] Fig. 6A is a partial schematic cross-sectional view of a thermal detector according to one embodiment;

[0041] Figure 6B yes Fig. 6A Another partial schematic cross-sectional view of the thermal detector shown in ;

[0042] Figure 6C yes Fig. 6A A top view of the thermal detector shown in ;

[0043] Fig. 7A is a partial schematic cross-sectional view of a thermal detector according to one embodiment;

[0044] Figure 7B yes Fig. 7A A top view of the thermal detector shown in FIG. DETAILED DESCRIPTION

[0045] In the drawings and the rest of the specification, the same reference numerals represent the same or similar elements. In addition, the various elements are not shown to scale to ensure that the drawings are as clear as possible. In addition, different embodiments and variations are not mutually exclusive and can be combined together. Unless otherwise specified, the terms "substantially", "approximately", "about" refer to within a margin of 10%, preferably within a margin of 5%. In addition, unless otherwise specified, the terms "between ... and ..." and the like are meant to include boundaries.

[0046] The invention relates to a wide detection spectrum band Δλ tot A thermal detector for electromagnetic radiation (e.g. infrared radiation or terahertz radiation) over the entire spectral band Δλ tot It has uniform high absorption, that is, the absorption spectrum α tot (λ) in the entire spectral band Δλ tot has a value at least equal to a predetermined threshold. For example, the detection spectral band Δλ tot At least the LWIR range (8 μm to 12 μm) is covered, and in particular extends to shorter wavelengths.

[0047] The thermal detectors may be part of a detector matrix in a detection device, wherein the thermal detectors are identical and arranged periodically. The thermal detectors each have an absorbing film which is suspended above the same readout substrate.

[0048] The absorbing film has at least two Salisbury absorbers, the at least two Salisbury absorbers are thermally coupled to the same thermometer transducer (so that heat from the absorber is transferred to the transducer), the at least two Salisbury absorbers define at least two quarter-wave cavities with the same reflector of the readout substrate. The resonant wavelength of at least one of the quarter-wave cavities is equal to the anti-resonant wavelength of the other quarter-wave cavity ±2 μm.

[0049] In other words, as explained in detail below, the absorbing film is designed so that the first quarter-wave cavity C 1 Optimize the first absorber at the resonant wavelength λ c1 (The absorption spectrum band of the first absorber Δλ 1 Therefore, the first absorber and the reflector have an absorption at a wavelength equal to λ c1 / 4n eq1 The vertical distance h 1 Interval, where n eq1 is with the quarter-wave cavity C 1 The equivalent refractive index of the associated medium (ie the medium positioned perpendicular to the first absorber and the reflector) and the medium of the absorbing film located on the first absorber and perpendicular to the first absorber.

[0050] In addition, the absorbing film is designed so that the second quarter-wave cavity C 2 Optimize the second absorber at the resonant wavelength λ c2 (The absorption band of the second absorber Δλ 2 Therefore, the second absorber and the reflector have an absorption at a wavelength equal to λ c2 / 4n eq2 The vertical distance h 2 Interval, where n eq2 is with the quarter-wave cavity C 2 The equivalent refractive index of the associated medium. Choose the distance h 2 and / or refractive index n eq2 , so that the resonant wavelength λ c2 Equal to the quarter wave cavity C 1 The anti-resonance, λ c1 / 2, error within plus or minus 2μm: λ c2 =λ c1 / 2±2μm, or λ c1 / 2-2μm≤λ c2 ≤λ c1 / 2+2μm. Therefore, in this way, the detection spectrum band of the thermal detector Δλ tot is broadened so that the detection band of the thermal detector is at least in two absorption bands Δλ 1 and Δλ 2 Extend upward.

[0051] In addition, in order to make the absorption spectrum of the thermal detector α tot (λ) in the entire detection spectral band Δλ tot The surface area ratio S between absorbers has a uniform high value. i / S j Between 0.5 and 3, where the surface area S i The total surface area of ​​the absorber corresponding to level i is such that its resonant wavelength is substantially equal to (±2 μm) the antiresonant wavelength of the absorber of level j. Therefore, in terms of spectral response, each absorber contributes to the total absorption spectrum α tot The contributions of (λ) are balanced, which ensures that the total absorption is within the entire detection spectral band Δλ tot The surface area S of the absorber is defined as the total surface area of ​​the absorber, that is, located at a constant distance h from the reflector in the quarter-wave cavity in question.

[0052] Figure 2A is a thermal detector 1 of electromagnetic radiation (in this case infrared radiation) according to one embodiment along the section line AA (see Figure 2B ) is a partial schematic cross-sectional view of the . Figure 2B yes Figure 2AA partial schematic top view of the thermal detector 1 shown in FIG.

[0053] A three-dimensional direct reference system XYZ is defined here and used for the rest of the description, wherein the plane XY is substantially parallel to the plane of the read-out substrate 10 of the thermal detector 1, the axis Z is oriented in a direction substantially orthogonal to the plane XY of the read-out substrate 10, and the plane XY is in the direction of the absorption film 20. Furthermore, the terms "lower" and "upper" are understood to relate to a positioning that increases when moving away from the read-out substrate 10 in the +Z direction.

[0054] The readout substrate 10 comprises a supporting substrate 11 containing a readout circuit (not shown) designed to control and read the thermal detector 1. The readout circuit can be in the form of a CMOS integrated circuit. Thus, the readout circuit has conductive parts flush with the top surface of the readout substrate 10, which is substantially flat. The conductive parts and the conductive vias can in particular be made of copper, aluminum and / or tungsten, for example by means of a damascene process in which trenches etched in the intermetallic insulating layer are filled.

[0055] The thermal detector 1 has a reflector 12 which rests on or in the readout substrate 10. The reflector is designed to reflect the electromagnetic radiation to be detected in the direction of the absorber film 20 and is preferably made of at least one metallic material. The reflector may be covered by the protective layer, which is made of a material that is substantially inert to the etchant subsequently used to remove the sacrificial layer or layers used to produce the suspended film 20 and the encapsulation structure that defines the vacuum cavity in which the absorber film 20 is located. The reflector 12 extends in the plane XY below the absorber film 20, in particular below the absorber located in the absorber film.

[0056] The thermal detector 1 has an absorbing film 20 which is suspended above the readout substrate 10 by anchoring posts 2 and is thermally insulated from the readout substrate 10 by holding thermally insulating arms 3. The anchoring 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 lower insulating layer 21 (e.g., Al 2 O 3 or amorphous silicon), polarized conductor tracks 22 (eg TiN or NiCr) and an upper insulating layer 23 (eg Al 2 O 3 or amorphous silicon) stack.

[0057] The absorption film 20 has a thermometer transducer 23 (in this case formed by a thermistor layer, i.e. a layer made of a material whose electrical resistance changes depending on its heating), a polarization electrode and at least two absorbers 31 , 32 , which are thermally coupled to the same thermometer transducer 23 .

[0058] In this example, the absorption film 20 has a lower insulating layer 21, which is made of, for example, a dielectric material (such as aluminum oxide, silicon oxide and / or silicon nitride), or an unintentionally doped semiconductor material (such as amorphous silicon). The lower insulating layer can have a thickness, for example, between 5nm and 100nm, preferably between 15nm and 50nm.

[0059] The polarization electrodes rest against the lower insulating layer 21. The polarization electrodes are made of a conductive material (in this case, in particular a metal material, such as TiN or NiCr), the polarization electrodes having a thickness, for example, between 5 nm and 15 nm, preferably between 6 nm and 10 nm. As described below, these polarization electrodes form a so-called lower thin-film absorber 32 here. Alternatively, however, the lower absorber can be separated from the polarization electrodes. Preferably, the material and thickness of the lower absorber 32 are selected so that the surface resistance of the lower absorber is substantially equal to the impedance of free space.

[0060] The lower absorber 32 is thus formed of two spatially distinct portions 32.1 and 32.2 extending from the holding arm 3 to the edge of the thermometer transducer 23 to enable electrical polarization of the lower absorber. In this example, each portion of the lower absorber 32 extends in a C-shape, thereby extending over a large portion of the absorber film 20. On the other hand, at the thermometer transducer 23, the two portions 31.1 and 31.2 are sufficiently spaced apart laterally in the XY plane so that the two portions are not perpendicular to the upper absorber 32. The surface area S of the lower absorber 32 is 2 corresponds to the sum of the surface areas of the two separate parts 32.1, 32.2. In this case, each part of the lower absorber 32 extends continuously with a constant thickness. Alternatively, each part of the lower absorber may extend discontinuously and have a non-constant thickness.

[0061] The lower absorber 32 is located at a substantially constant distance h from the reflector 12. 2 At, thus forming the resonant wavelength λ c2 The quarter wave cavity C 2 , where h 2 =λ c2 / 4n eq2 Wavelength λ c2 is the spectral band Δλ tot The spectral subband Δλ 2 Here, n eq2 is with the quarter-wave cavity C 2The equivalent refractive index of the associated medium, that is, the medium located vertically above the lower absorber 32, between the lower absorber and the reflector 12, and the medium located on the lower absorber 32 and vertically above the lower absorber. As described in detail below, the distance h is selected 2 and / or refractive index n eq2 , so that the wavelength λ c2 Equal to (within plus or minus 2 μm) a quarter-wave cavity C 1 The anti-resonance wavelength λ c1 / 2.

[0062] In this case, the thermometer transducer 23 extends over the polarization electrode and the lower insulating layer 21 and contacts the polarization electrode and the lower insulating layer. The thermometer transducer is a thermistor material, and its thickness is, for example, about tens of nanometers to hundreds of nanometers. The thermometer transducer can be a material containing vanadium or titanium oxide or amorphous silicon. Alternatively, the thermometer transducer can also be a diode (pn or pin junction) or a metal oxide semiconductor field effect transistor (MOSFET), etc.

[0063] The upper protective layer 24 covers the thermometer transducer 23, in this case only on the upper surface of the thermometer transducer, but the upper protective layer can completely cover the thermometer transducer to protect the thermometer transducer 23 from possible contamination or damage during the steps of the manufacturing method. The upper protective layer can be made of an electrically insulating material (for example a dielectric material, such as silicon oxide, nitride or oxynitride, or even aluminum oxide) with a thickness of several tens of nanometers.

[0064] The absorption film 20 has a second absorber 31 (so-called upper absorber), which is formed by a thin film made of at least one material designed to absorb the electromagnetic radiation to be detected, such as a metallic material, in particular such as TiN or NiCr, with a thickness of, for example, between 5 nm and 15 nm, preferably between 6 nm and 10 nm. The upper absorber 31 is thermally coupled to the thermometer transducer 23. Here, the upper absorber rests on the upper protective layer 24 and does not extend relative to the lower absorber 32 (vertically), so as to prevent weakening of the absorption of electromagnetic radiation by one or the other of the absorbers.

[0065] Preferably, the material and thickness of the upper absorber 31 are selected so that the surface resistance of the upper absorber is substantially equal to the impedance of free space. In this case, the upper absorber extends continuously with a constant thickness. Alternatively, the upper absorber may extend discontinuously and have a non-constant thickness. 1 is the total surface area of ​​the upper absorber 31 .

[0066] The upper absorber 31 is located at a substantially constant distance h from the reflector 12. 1 At, thus forming the resonant wavelength λc1 The quarter wave cavity C 1 , where h 1 =λ c1 / 4n eq1 Wavelength λ c1 is the spectral band Δλ tot The spectral subband Δλ 1 Here, n eq1 is with the quarter-wave cavity C 1 The equivalent refractive index of the associated medium, that is, the medium located vertically above the upper absorber 31, between the upper absorber and the reflector 12, and the medium located on the upper absorber 31 and vertically above the upper absorber.

[0067] According to the invention, the absorption film 20 therefore has at least two Salisbury absorbers 31 , 32 , which are designed to absorb the detection spectral band Δλ tot The absorbing film is designed to make the quarter-wave cavity C 2 The associated resonant wavelength λ c2 Equal (within plus or minus 2 μm) to the quarter-wave cavity C 1 The associated antiresonance wavelength λ c1 / 2. This configuration can be adjusted by adjusting the distance h 1 and h 2 or by adjusting the equivalent refractive index n eq1 and n eq1 One and / or the other (by choice of material and thickness) may be achieved.

[0068] Therefore, the total absorption spectrum α of the thermal detector 1 is tot (λ) corresponds to the absorption spectrum α of the upper absorber 31 1 (λ) and the absorption spectrum α of the lower absorber 32 2 The sum of (λ). Detection spectral band Δλ tot No longer affected by the quarter-wave cavity C 1 The anti-resonance limit does not appear to be limited by the quarter-wave cavity C 2 The anti-resonance limit (see below) Figure 3B described in detail).

[0069] In addition, the surface area ratio S 2 / S 1 is between 0.5 and 3, preferably between 0.8 and 2, and preferably equal to about 1. In this way, each absorber 31, 32 contributes to the total absorption spectrum α of the thermal detector 1 tot The contribution of (λ) is balanced, which results in tot Uniform high absorption value αtot (at least equal to the predetermined threshold α tot，th ).

[0070] It should be noted that the lower absorber 32, which in this case also forms a polarizing electrode, has a much larger total surface area than in the prior art where the electrodes were narrow tracks and did not form a Salisbury absorber.

[0071] To illustrate the total absorption spectrum α of the absorbers 31 and 32 to the thermal detector 1 tot (λ), now consider Figure 3A Two absorbers 31 , 32 and a reflector 12 are schematically shown in FIG. Figure 3B , Figure 4A and Figure 4B The total absorption spectrum α of the absorption film 20 is shown. tot (λ) and those of the upper absorber 31 and the lower absorber 32 1 (λ) and α 2 (λ) example, where the surface area ratio S 2 / S 1 Equal to about 1( Figure 3B ), equal to about 0.5( Figure 4A ) and equal to approximately 2( Figure 4B ).

[0072] In this example, the lower absorber 32 is made of TiN with a thickness of 8 nm and extends as a square ring in the plane XY. In this case, the lower absorber is vertically spaced apart from the reflector 12 by a distance h equal to 1.5 μm. 2 . In addition, the upper absorber 31 is made of TiN with a thickness of 8 nm, and the upper absorber extends in a square shape in the plane XY. In this case, the size of the upper absorber is equal to the size of the empty inner space of the lower absorber 32. In this case, the upper absorber is vertically spaced apart from the reflector 12 by a distance h equal to 2.5 μm. 1 =h 2 +δ. In addition, in this case, the pixel pitch is equal to 12 μm, and from the relationship ff=(S 2 +S 1 ) / p 2 The defined filling factor ff is equal to 80%.

[0073] Here the absorption spectra are obtained by numerically solving Maxwell's equations using finite elements.

[0074] Absorption spectrum α of the upper absorber 31 1 (λ) at the resonant wavelength λ c1, which is equal to about 13 μm, and decreases sharply at the antiresonance wavelength of about 5 μm. In addition, the absorption spectrum α of the lower absorber 32 is 2 (λ) at the resonant wavelength λ c2 has a maximum value near , which is equal to about 6 μm, and decreases sharply at the antiresonance wavelength of about 3 μm. tot (λ) does not seem to drop as sharply at the anti-resonance wavelengths of 5 μm (absorption about 60%) and 3 μm (absorption about 40%).

[0075] In addition, since the surface area is larger than S 2 / S 1 = 1, the contribution of each absorber 31, 32 is uniform here, so that the total absorption spectrum α tot (λ) in the entire detection spectral band Δλ tot Therefore, if the threshold absorbance is assumed to be 40%, the detection spectral band Δλ tot The range of the detection spectral band is from 3 μm to more than 20 μm. If the threshold absorption value is assumed to be 60%, the range of the detection spectral band is from 5 μm to more than 20 μm. And if the threshold absorption value is assumed to be 80%, the range of the detection spectral band is from 6 μm to 15 μm. Therefore, the detection spectral band Δλ tot is significantly broadened, and the total absorption spectrum α tot (λ) is uniformly high, i.e., over the entire spectral band Δλ tot At least equal to the threshold.

[0076] It should be noted here that the maximum lateral dimension of the absorbers 31, 32 is less than or equal to the detection spectral band Δλ tot In this example, for the spectral band Δλ from 6 μm to 15 μm tot (80% threshold absorption value), the maximum lateral dimension of the absorbers 31, 32 is equal to about 11 μm. Here, the upper absorber 31 is in the shape of a square with a side length of 7.6 μm, and the lower absorber 32 is in the shape of a square ring with a side length of 10.7 μm. In addition, the lateral dimension of the absorber is smaller than the central wavelength of 11 μm.

[0077] This configuration therefore appears to maximize the optical collection efficiency of the incident electromagnetic radiation. In fact, although the relative surface area of ​​the upper absorber 31 is 40%, the absorption of the upper absorber 31 is as high as 65% near the resonance wavelength of 13 μm of the upper absorber. Similarly, although the relative surface area of ​​the lower absorber 32 is also 40%, the absorption of the lower absorber 32 is as high as 60% near the resonance wavelength of 5 μm of the lower absorber. The association of two absorbers 31, 32 covering 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 μm and 15 μm.

[0078] By surface area ratio S 2 / S 1 To adjust each absorption spectrum α 1 (λ) and α 2 (λ) contribution, which can modify the overall absorption spectrum of thermal detector 1 α tot (λ).

[0079] When the surface area ratio S 2 / S 1 When it is equal to 0.5 (see Figure 4A ), the contribution of the lower absorber 32 is reduced here, which is beneficial to the contribution of the upper absorber 31. And when the surface area ratio S 2 / S 1 When it is equal to 2 (see Figure 4B ), the contribution of the lower absorber 32 is increased at the expense of the contribution of the upper absorber 31.

[0080] Therefore, when the threshold absorption value is equal to 60%, the absorption spectrum band Δλ tot The range is from 6μm to more than 20μm, where S 2 / S 1 =0.5( Figure 4A ), with a maximum absorption of 90% near 12 μm. On the other hand, the absorption band ranges from 4 μm to 20 μm, where S 2 / S 1 =2( Figure 4B ), with the maximum absorption being 90% near 7μm to 8μm.

[0081] Figure 5A Shown in Figure 3A Example total absorption spectrum for the configuration shown in α tot (λ) with surface area ratio S 2 / S 1 changes, and Figure 5B shows the total absorption spectrum α tot (λ), where S 2 / S 1 =0.5, S 2 / S1 =3, S 2 / S 1 Very small (S 2 / S 1 <<1: upper absorber 31 fills the entire available surface area) and S 2 / S 1 Very large (S 2 / S 1 >>1: Lower absorber 32 fills the entire available surface area).

[0082] For S 2 / S 1 Very small total absorption spectrum α tot (λ), spectrum in quarter-wave cavity C 1 The peak value is shown at the antiresonance wavelength (i.e., around 5 μm). Similarly, for S 2 / S 1 Very large total absorption spectrum α tot (λ), spectrum in quarter-wave cavity C 2 The peak value is shown at the anti-resonance wavelength (i.e., around 3 μm). tot These absorption limits are not found in (λ), where S 2 / S 1 =0.5 and S 2 / S 1 =3.

[0083] Fig. 6A and Figure 6B is a partial schematic diagram of a thermal detector 1 for electromagnetic radiation according to one embodiment, Fig. 6A and Figure 6B They are respectively along the section line AA and the section line BB (see Figure 6C ) cross section. Figure 6C yes Fig. 6A and Figure 6B A top view of the thermal detector 1 is shown in FIG.

[0084] In this example, the absorbing film 20 has an identical thermometer transducer 23 which is thermally coupled to more than two absorbers, in this case three absorbers 31, 32, 33 which form three separate quarter-wave cavities C in terms of the absorption spectral band. 1 , C 2 , C 3 .

[0085] The absorption film 20 here has: a lower insulating layer 21; a thin metal film in two spatially different parts in the plane XY, which forms a polarization electrode and a second absorber 32 and a third absorber 33; an upper insulating layer 22; a thermometer transducer 23 (in this case a thermistor material layer), which rests on the upper insulating layer and passes through the upper insulating layer at the opening 22a to make contact with the metal layer; an upper protective layer 24, which covers the thermometer transducer 23; and a thin metal film, which rests on the thermometer transducer 23 and forms a first absorber 31 (upper absorber).

[0086] The upper absorber 31 is located on the thermometer transducer 23 at a distance h 12 from the reflector. 1 Quarter wave cavity C 1 This enables optimization of the upper absorber 31 in the spectral band Δλ 1 The wavelength λ c1 The dielectric of the quarter-wave cavity comprises in particular an upper protective layer 24, a thermistor material 23 and two insulating layers 22, 21. Figure 6C As shown, the upper absorber 31 extends over only a portion of the surface of the thermometer transducer 23, in this case the upper absorber extends over approximately half of the surface of the thermometer transducer.

[0087] In addition, the metal layer formed of two parts (the two parts serve as polarization electrodes) forms a second absorber 32 (quarter wave cavity C 2 ), the second absorber is spaced apart from the reflector 12 by a distance h 2 In this quarter wave cavity C 2 In the embodiment, the second absorber 32 extends into the absorbing film 20 and is not covered by the thermometer transducer 23. The absorption of the second absorber 32 occurs at a wavelength λ c2 The spectral subband Δλ is centered 2 With the quarter wave cavity C 2 The associated medium here comprises, in particular, two insulating layers 21 , 22 .

[0088] In the third quarter-wave cavity C 3 In FIG. 1 , 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 parts 33.1 and 33.2 of the metal layer covered by the thermometer transducer 23 form the third absorber 33. The third absorber is spaced from the reflector 12 by the same distance h as the second absorber 32. 2 The absorption of the third absorber 33 occurs at a wavelength λ c3 The spectral subband Δλ is centered 3 With the quarter wave cavity C 3The associated medium here comprises in particular an upper protective layer 24 , a thermistor transducer 23 and two insulating layers 22 , 21 .

[0089] In this way, the three quarter-wave cavities C 1 , C 2 , C 3 The size depends on the height h 1 and h 2 (In this case, the distance h of the third absorber 3 Equal to h 2 ) and the equivalent refractive index n eq1 、n eq2 and n eq3 To obtain a wide detection spectral band Δλ tot , while maintaining the absorption value α tot is uniformly higher than the reference value. In this way, the quarter-wave cavity C 2 can be designed in a quarter-wave cavity C 1 The quarter-wave cavity C 3 can be designed to be between Δλ 1 and Δλ 2 The spectral band between 3 For example, by adjusting the quarter-wave cavity C 3 The thickness of this layer of the absorption film 20 is used for absorption.

[0090] Fig. 7A is a cross-sectional view of a thermal detector 1 of electromagnetic radiation according to an embodiment along a cross-sectional line AA (see Figure 7B ) is a partial schematic cross-sectional view of the . Figure 7B yes Fig. 7A A top view of the thermal detector 1 is shown in FIG.

[0091] In this example, the absorbing film 20 has an identical thermometer transducer 23 thermally coupled to more than two absorbers, in this case five absorbers 31 , 32 , 33 , 34 and 35 , which form five separate quarter wave cavities in terms of absorption spectral bands.

[0092] The absorber film 20 here has: a lower insulating layer 21; a thin metal film in a plurality of spatially different portions in the plane XY, which forms polarization electrodes and a plurality of different absorbers; an upper insulating layer 22; a thermometer transducer 23 (in this case a layer of thermistor material) which rests on the upper insulating layer and passes through the upper insulating layer at openings 22a to contact the metal layer. An upper protective layer 24 covers the thermometer transducer 23.

[0093] Different parts of the thin metal film form different absorbers 31 to 35 and define a quarter wave cavity. In this example, there is no upper absorber resting on the thermometer transducer 23, but alternatively there may be such an upper absorber (in which case the thermometer transducer 23 would not cover the absorber).

[0094] The two central parts form a first absorber 31 which is spaced apart from the reflector 12 by a distance h 1 The two central parts are covered by the thermometer transducer 23 and are defined in the spectral band Δλ 1 has a resonant wavelength λ c1 The quarter wave cavity C 1 . With a refractive index of n eq1 The medium comprises in particular the temperature transducer 23 and the two insulating layers 21 , 22 .

[0095] The side portion forms a further absorber 35 which is spaced apart from the reflector 12 by the same distance h 1 This further absorber is not covered by the thermometer transducer 23 and it is limited to the spectral band Δλ 5 has a resonant wavelength λ c5 The quarter wave cavity C 5 . With a refractive index of n eq5 The medium comprises, in particular, two insulating layers 21 , 22 .

[0096] The other three side portions form different absorbers 32, 33, 34. The absorbers 32, 33, 34 are spaced apart from the reflector 12 by a distance h 2 、h 3 and h 4 , distance h 2 、h 3 and h 4 Different from each other and with the value h 1 They are not covered by the thermometer transducer 23, and their defined resonant wavelengths are λ c2 , c3 and λ c4 The quarter wave cavity C 2 , C 3 and C 4 . With a refractive index of n eq2 、n eq3 and n eq4 The dielectric basically consists of two insulating layers.

[0097] In addition, the absorption film has different heights at the locations where the absorbers 32, 33, 34 are located. Therefore, the absorbers 32, 33, 34 have flat portions, wherein the absorbers 32, 33, 34 are spaced apart from the reflector 12 by a corresponding distance h. 2 、h3 and h 4 , connected to the main flat portion where the thermometer transducer 23 is located through a vertical (as shown in the figure) or inclined connecting portion. Therefore, the flat portion where the absorbers 32, 33, 34 are located forms a step of the absorption film 20 relative to the main flat portion.

[0098] In this way, the absorbent film 20 at the height h 1 to h 5 and the equivalent refractive index n eq1 to n eq5 Aspects are designed to obtain a wide detection spectral band Δλ tot , while maintaining the absorption value α tot Uniformly above the reference value. Multiple quarter wave cavities can be designed to absorb optimally at the anti-resonance of other quarter wave cavities. Other quarter wave cavities can also be designed to absorb in spectral bands between the spectral bands of other quarter wave cavities.

[0099] Having just described specific embodiments, various changes and modifications will become apparent to those skilled in the art.

Claims

1. A thermal detector (1) configured to absorb a predetermined spectral band Δλ tot In the electromagnetic radiation, the heat detector has: o a readout substrate (10) having: a readout circuit; and a reflector (12) configured to reflect the electromagnetic radiation; an absorbing film (20) suspended above the readout substrate (10), the absorbing film being thermally insulated from the readout substrate (10), the absorbing film having a thermometer transducer (23), the thermometer transducer being electrically connected to the readout circuit, and the absorbing film having: a first thin film absorber (31), said first thin film absorber having a total surface area S1, ■ the first thin film absorber is thermally coupled to the thermometer transducer (23), ■ The first thin film absorber is configured to absorb the spectral band Δλ tot The wavelength λ c1 The electromagnetic radiation in the spectral sub-band Δλ1 centered at the center thereof, and the first thin film absorber is spaced from the reflector (12) by a distance equal to λ c1 / 4n eq1 The value h1 forms a wavelength λ with the reflector c1 The first quarter-wave cavity C1,n eq1 is the refractive index of the medium associated with the first quarter-wave cavity C1; at least one second thin film absorber (32), the at least one second thin film absorber having a total surface area S2, ■ said at least one second thin film absorber is thermally coupled to said thermometer transducer (23), ■ the at least one second thin film absorber is arranged in the absorber film (20) so as not to be covered by the first absorber (31), ○It is characterized by: The second absorber (32) is configured to absorb the spectral band Δλ tot The wavelength λ c2 The electromagnetic radiation in the spectral sub-band Δλ2 centered at the center thereof, and the second absorber and the reflector (12) are spaced apart by a distance equal to λ c2 / 4n eq2 The value h2 forms a wavelength λ with the reflector c2 The second quarter-wave cavity C2, n eq2 is the refractive index of the medium associated with the second quarter-wave cavity C2, the spectral sub-band Δλ2 is at wavelength λ c2 Centered at wavelength λ c2 Equal to λ c1 / 2 (within plus or minus 2μm), ○The first absorber (31) and the second absorber (32) have a total surface area such that the surface area ratio S2 / S1 is between 0.5 and 3.

2. The thermal detector (1) according to claim 1, wherein: The first absorber (31) abuts against the thermometer transducer (23).

3. The thermal detector (1) according to claim 1, wherein: The second absorber (32) extends into the absorption film (20) without being covered by the thermometer transducer (23).

4. The thermal detector (1) according to claim 3, wherein: The second absorber (32) is formed by a plurality of parts (32.1, 32.2) of a metal layer, which on the one hand forms a polarization track at the retaining arm (3) and on the other hand forms a polarization electrode, the polarization track ensuring support and thermal insulation of the absorption film (20), the polarization electrode being in contact with the thermometer transducer (23).

5. The thermal detector (1) according to claim 4, wherein: The metal layer extends in a planar manner into the retaining arm (3) and into the absorption film (20).

6. The thermal detector (1) according to claim 1, comprising a third absorber (33) configured to absorb the spectral band Δλ tot The wavelength λ c3 The electromagnetic radiation in the spectral sub-band Δλ3 centered at the third absorber is spaced apart from the reflector (12) by a distance equal to λ c3 / 4n eq3 The value h3 forms a wavelength λ with the reflector c3 The quarter-wave cavity C3, n eq3 is the refractive index of the medium associated with the quarter-wave cavity C3, wavelength λ c3 Between wavelength λ c1 To wavelength λ c2 between.

7. The thermal detector (1) according to claim 6, wherein: The distance h3 is equal to the distance h2, and the third absorber (33) is covered by the thermometer transducer (23).

8. The thermal detector (1) according to claim 1, comprising at least one absorber, wherein the at least one absorber is configured to absorb the spectral band Δλ tot The wavelength λ c4 The at least one absorber and the reflector (12) are spaced apart by a distance equal to λ. c4 / 4n eq4 The value h4 forms a wavelength λ with the reflector c4 The quarter-wave cavity C4, n eq4 is the refractive index of the medium associated with the quarter-wave cavity C4, the absorber of the quarter-wave cavity C4 is located in the flat portion of the absorbing film (20), the flat portion forming a step relative to the main plane, in which the metal layer extends to form a polarization track located in the retaining arm (3) and a polarization electrode in contact with the thermometer transducer (23).

9. The thermal detector (1) according to claim 1, wherein: Detection spectral band Δλ tot Includes the spectral band LWIR ranging from 8μm to 12μm.

10. The thermal detector (1) according to claim 1, wherein the thermal detector detects tot The absorption on is at least equal to 80%.

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