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, comprising at least one thermal detector with an absorbing membrane suspended above a readout substrate. The invention is particularly applicable in the fields of infrared imaging, thermography and, inter alia, gas detection. [Background technology]

[0002] The device for detecting electromagnetic radiation may 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 insulation of the thermometer transducer from the readout substrate, the absorbing film is usually suspended above the readout substrate by anchor posts and is thermally insulated from the readout substrate by holding arms. These anchor posts and holding arms also have an electrical function by connecting the absorbing film to a readout circuit, which is generally located on the substrate. The absorbing film has an absorber, for example 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 absorptive 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 absorptive membrane 20 to readout circuitry located on the readout substrate 10.

[0005] The film 20 comprises 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 may be a material that has an electrical resistance that changes as it heats up (thermistor). It may in particular be amorphous silicon or vanadium oxide. 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 by the absorbing film 20 of the electromagnetic radiation to be detected. Such an absorber is therefore commonly called a Salisbury absorber.

[0006] The 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 where λ is the thin film absorber spaced at a distance h equal to 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 effective refractive index of the medium associated with the quarter-wave cavity. The absorber is generally 0 =377 Ω.

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

[0008] In the second configuration, the polarizing 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 polarizing electrodes. In this way, the absorber does not vertically cover the polarizing electrodes. This therefore reduces the spectral band of detection Δλ if material is present in the quarter-wave cavity.tot The central wavelength λ c1 , is spaced perpendicularly from the reflector at a distance such that absorption is optimum for

[0009] However, while maintaining a uniformly high absorptance (e.g., at least 70% across the entire spectral band of detection), particularly at shorter wavelengths, 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 spectral band of detection 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] An 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] US Patent Application Publication No. 2010 / 0148067 Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0014] To achieve this, an object of the present invention is a thermal detector of electromagnetic radiation within a predetermined spectral band Δλ tot which comprises a readout substrate having a readout circuit and a reflector designed to reflect electromagnetic radiation, an absorptive film insulated from the readout substrate and suspended above the readout substrate, having a thermometer transducer electrically connected to the readout circuit, thermally coupled to the thermometer transducer, designed to absorb electromagnetic radiation within a spectral sub-band Δλ c1 centered on a wavelength λ tot of the spectral band Δλ 1 and forming a first quarter-wave cavity C c1 for the wavelength λ 1 separated from the reflector by a value h c1 equal to λ eq1 / 4n 1 where n eq1 is the refractive index of the medium associated with the first quarter-wave cavity C 1 and having a first thin-film absorber with a total surface area S 1 , at least one second thin-film absorber thermally coupled to the thermometer transducer, having a total surface area S 2 and arranged on the absorptive film so as not to be covered by the first absorber, and an absorptive film having .

[0015] According to the present invention, the second absorber has a wavelength λ c2 Spectral band Δλ centered at tot Spectral subbands Δλ 2 It is designed to absorb electromagnetic radiation within the wavelength λ c2 A second quarter-wave cavity for C 2 λ to form c2 / 4n eq2 A value equal to h 2 The reflector is located at a distance of n eq2 is the second quarter-wave cavity C 2 is the refractive index of the medium related to the spectral subband Δλ 2 is λ c1 / 2 is equal to within ±2 μm of the wavelength λ c2 Centered on.

[0016] The first and second absorbers have a surface area ratio S 2 / S 1 is included 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 absorbent body may extend into the absorbent membrane without being covered by the thermometer transducer.

[0020] The second absorber can be formed by portions of a metal layer which, on the one hand, form polarizing tracks at the holding arms which ensure support and thermal insulation of the absorbent membrane, and, on the other hand, form polarizing electrodes which 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 Spectral band Δλ centered at totSpectral subbands Δλ 3 It is designed to absorb electromagnetic radiation within the wavelength λ c3 Quarter-wave cavity for C 3 λ to form c3 / 4n eq3 A value equal to h 3 The reflector is located at a distance of n eq3 is a quarter wave cavity C 3 is the refractive index of the medium related to the wavelength λ c3 is the wavelength λ c1 and λ c2 and a third absorber located between the first and second absorbers.

[0023] distance h 3 is the distance h 2 and the third absorber is covered by the thermometer transducer.

[0024] The thermal detector detects the wavelength λ c4 Spectral band Δλ centered at tot Spectral subbands Δλ 4 It is designed to absorb electromagnetic radiation within the wavelength λ c4 Quarter-wave cavity for C 4 λ to form c4 / 4n eq4 A value equal to h 4 The reflector is located at a distance of n eq4 is a quarter wave cavity C 4 The quarter-wave cavity C can have at least one absorber, where C is the refractive index of the medium related to 4 The absorber may be in a flat portion of an absorbing film forming a step relative to the main plane extending the metal layer forming the polarizing track arranged on the holding arm and the polarizing electrode in contact with 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 Δλtot 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 description 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] FIG. 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. [Figure 4A] FIG. 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] FIG. 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. 13 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] FIG. 5B shows several total absorption spectra αtot(λ) of the thermal detector for different values ​​of the absorber surface area ratio S2 / S1 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 PREFERRED EMBODIMENTS

[0029] In the figures, and in the remainder of the description, the same reference numerals represent the same or similar elements. In addition, the various elements are not 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 boundaries are included, unless otherwise stated.

[0030] The present invention provides a wide detection spectral band Δλ tot For thermal detectors of electromagnetic radiation in the spectral band Δλ tot The absorption rate is uniformly high throughout the entire 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 tot covers at least the LWIR range (8-12 μm) and especially the 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 membrane 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 in the readout substrate, at least one of the quarter-wave cavities having a resonant wavelength equal to plus or minus 2 μm of the anti-resonant wavelength of another of the quarter-wave cavities.

[0033] In other words, as described in detail below, the absorbing film is a first quarter-wave cavity C 1 is the resonant wavelength λ c1 (Absorption spectrum band Δλ of the first absorber 1 The first absorber is designed to optimize the absorption at a wavelength of λ c1 / 4n eq1 A vertical distance h equal to 1 away from the reflector at eq1 is a quarter wave cavity C 1 is the equivalent refractive index of the media associated with the first absorber and the reflector, i.e., the medium of the absorbing film placed perpendicularly on the first absorber.

[0034] The absorbing membrane also forms a second quarter-wave cavity C 2 is the resonant wavelength λ c2 (Absorption band Δλ of the second absorber 2 The second absorber is designed to optimize the absorption of the second absorber at a wavelength of λ c2 / 4n eq2 A vertical distance h equal to 2 away from the reflector at eq2 is a quarter wave cavity C 2 is the effective refractive index of the medium related to the distance h 2 and / or the refractive index n eq2 is the resonant wavelength λ c2 But, quarter wave cavity C 1 Anti-resonance of λ c1 / 2 within plus or minus 2 μm, i.e., λc2 = λc1 / 2 ± 2 μm, or λc1 Thus, the spectral band of detection Δλ tot Therefore, this has at least two absorption spectral bands Δλ 1 and Δλ 2 It extends as far as it can.

[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 is set to a uniformly high value throughout i / S j is included between 0.5 and 3, where the surface area S i corresponds 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). Thus, the total absorption spectrum α tot (λ) are balanced, so that the total absorption is 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, 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, and 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 absorbing film 20. Also, the terms "lower" and "upper" are understood as relating 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 which includes a readout circuit (not shown) designed to control and read out the thermal detector 1. The readout circuit may be in the form of a CMOS integrated circuit. It therefore has conductive parts which are planar with the top surface of the readout substrate 10, which is substantially flat. The conductive parts and conductive vias may be made, inter alia, of copper, aluminium and / or tungsten, for example by a damascene process, in which trenches etched in an intermetallic 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 in the direction of the absorbing membrane 20 and is preferably made from at least one metallic material. It can be covered by a protective layer made of a material that is substantially inert to the etchant subsequently used to remove the suspended membrane 20 as well as the sacrificial layer used to manufacture the encapsulation structure (which defines the vacuum cavity in which the absorbing membrane 20 is located). The reflector 12 extends in the plane XY below the absorbing membrane 20, and in particular below the absorber arranged therein.

[0040] The thermal detector 1 has an absorbent membrane 20 that is suspended above a readout substrate 10 by anchor posts 2 and insulated from the readout substrate 10 by a holding and insulating arm 3. The anchor posts 2 and holding arm 3 also provide electrical connections to the readout circuitry contained in the readout substrate 10. The holding arm 3 is supported by a lower insulating layer 21 (e.g. Al 2 O 3 or amorphous silicon), a polarized conductor track 32 (for example TiN or NiCr), and an upper insulating layer 22 (for example Al 2 O 3 or amorphous silicon).

[0041] The absorbent 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, polarizing electrodes and at least two absorbers 31, 32 thermally coupled to the same thermometer transducer 23.

[0042] In this example, the absorbing film 20 has 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] Polarizing electrodes rest on the lower insulating layer 21. They are made of an electrically conductive material, in this case in particular a metallic material such as TiN or NiCr, and have a thickness comprised for example between 5 and 15 nm, preferably between 6 and 10 nm. As will be explained below, these polarizing electrodes form here the so-called lower thin-film absorber 32. However, instead, the lower absorber may be separate from the polarizing electrodes. The material and thickness of the lower absorber 32 are preferably selected such 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 parts 32.1 and 32.2, which extend from the holding arm 3 to the edge of the thermometer transducer 23 so that the latter can be electrically polarized. In this example, each part of the lower absorber 32 extends in a C-shape so as to extend over most of the absorbent membrane 20. On the other hand, in the thermometer transducer 23, the two parts 32.1 and 32.2 are sufficiently spaced laterally in the XY plane so as not to be perpendicular to the upper absorber 31. The surface area S of the lower absorber 32 is 2corresponds to the sum of the surface areas of the two individual parts 32.1, 32.2. Each part of the lower absorbent body 32 extends continuously and with a constant thickness in the present case. Alternatively, it can extend discontinuously and have a non-constant thickness.

[0045] The lower absorber 32 is positioned at a substantially constant distance h from the reflector 12. 2 and hence the resonant wavelength λ c2 Quarter-wave cavity C 2 where h 2 = λ c2 / 4n eq2 Wavelength λ c2 is the spectral band Δλ tot Spectral subbands Δλ 2 where n eq2 is a quarter wave cavity C 2 is the equivalent refractive index of the medium associated with the distance h, i.e., the medium located vertically above the lower absorber 32, between the lower absorber 32 and the reflector 12, as well as the medium located on and vertically above the lower absorber 32. 2 and / or the refractive index n eq2 is the wavelength λ c2 is a quarter wave cavity C 1 The anti-resonant wavelength λ c1 / 2 to within plus or minus 2 μm.

[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 of the order of a few dozens to hundreds of nanometers in thickness. 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] A top 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 steps of the manufacturing method. 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 made 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 comprised 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 the upper protective layer 24 and does not extend oppositely (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. It extends continuously and with a constant thickness in the present case. Alternatively, it can extend discontinuously and have a non-constant thickness. 1 is the total surface area of ​​the upper absorbent body 31.

[0050] The upper absorber 31 is positioned at a substantially constant distance h from the reflector 12. 1 and hence the resonant wavelength λ c1 Quarter-wave cavity C 1 where h 1 = λ c1 / 4n eq1 Wavelength λ c1 is the spectral band Δλ tot Spectral subbands Δλ 1 where n eq1 is a quarter wave cavity C 1is the equivalent refractive index of the media related to the reflector 12, i.e. the medium located vertically above the upper absorber 31, between the upper absorber 31 and the reflector 12, as well as the media located on and vertically above the upper absorber 31.

[0051] According to the invention, the absorbing film 20 is therefore adapted to detect the spectral band Δλ tot The Salisbury absorber 31, 32 is designed to absorb electromagnetic radiation within a quarter-wave cavity C. 2 The resonant wavelength λ related to c2 But, quarter wave cavity C 1 The anti-resonant wavelength λ related to c1 This configuration is designed to be equal to the distance h 1 and h 2 or (by material and thickness selection) 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) is the absorption spectrum α of the upper absorber 31 1 (λ) and the absorption spectrum α of the lower absorber 32 2 (λ) corresponds to the sum of the spectral bands of detection Δλ tot It is no longer a quarter wave cavity C 1 , which is limited by the anti-resonance of the quarter-wave cavity C (as described in more detail below with reference to FIG. 3B). 2 It also does not appear to be limited by anti-resonance.

[0053] In addition, the surface area ratio S 2 / S 1 is comprised between 0.5 and 3, preferably between 0.8 and 2, and is preferably approximately equal to 1. Thus, the total absorption spectrum α tot The contribution of each absorber 31, 32 to (λ) is balanced, resulting in a spectral band Δλ totat least a predetermined threshold value α tot,th A uniformly high absorption value α equal to tot This results in:

[0054] It should be noted that the lower absorber 32, which in the present case also forms a polarizing 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 the absorbers 31, 32 to (λ), we now consider two absorbers 31, 32 and a reflector 12 as shown diagrammatically in Figure 3A. Figures 3B, 4A and 4B show the total absorption spectrum α tot (λ) and the α 1 (λ) and α 2 (λ), where the surface area ratio S 2 / S 1 is approximately equal to 1 (Figure 3B), approximately equal to 0.5 (Figure 4A), and approximately equal to 2 (Figure 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 apart by a distance h 2 The upper absorber 31 is vertically spaced from the reflector 12 by a distance h , which in this case is equal to 2.5 μm. Furthermore, the upper absorber 31 is made of TiN with a thickness of 8 nm and extends in the plane XY in a rectangular shape. Its dimensions are equal in this case to the empty inner space of the lower absorber 32. 1 =h 2 +δ from the reflector 12. Furthermore, the pixel pitch is equal to 12 μm in this case, and the equation ff=(S 2 +S 1 ) / p 2 The fill factor ff defined by is equal to 80%.

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

[0058] Absorption spectrum α of the upper absorber 31 1 (λ) is the resonant wavelength, λ, which here is equal to approximately 13 μm c1 The absorption spectrum α of the lower absorber 32 has a maximum value around 0.01 μm and decreases sharply at the antiresonant wavelength of about 5 μm. 2 (λ) is the resonant wavelength, λ, which here is equal to approximately 6 μm c2 The absorption spectrum has a maximum value around α and decreases rapidly at the antiresonant wavelength of about 3 μm. 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] The contribution of each absorber 31, 32 is the surface area ratio S 2 / S 1 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 tot ranges from 3 μm to more than 20 μm. If it is assumed to be 60%, then it ranges from 5 μm to more than 20 μm. If it is assumed to be 80%, then it ranges from 6 to 15 μm. Thus, the spectral band of detection Δλ tot is quite broad, 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 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 the optical collection of the 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 joint of the 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 and 15 μm.

[0062] Each absorption spectrum α 1 (λ) and α 2 (λ) by the surface area ratio S 2 / S 1 The total absorption spectrum of thermal detector 1 by adjusting via α tot It is possible to modify (λ).

[0063] Surface area ratio S 2 / S 1 When the surface area ratio S 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. 2 / S 1 When is equal to 2 (see FIG. 4B), the contribution of the lower absorbent body 32 increases at the expense of the upper absorbent body 31.

[0064] Therefore, when the absorption threshold is equal to 60%, S 2 / S 1 = 0.5 (Figure 4A) and the maximum absorptance is 90% around 12 μm, the absorption spectral band Δλ tot ranges from 6 μm to more than 20 μm. 2 / S 1= 2 (Figure 4B), where the maximum absorption is 90% around 7-8 μm, this ranges from 4 μm to 20 μm.

[0065] FIG. 5 shows the surface area ratio S 2 / S 1 Exemplary total absorption spectra α as a function of tot (λ), and FIG. 5B shows S 2 / S 1 If =0.5, S 2 / S 1 = 3, and S 2 / S 1 is very small (S 2 / S 1 <<1, where the upper absorbent body 31 fills the entire available surface area), and S 2 / S 1 is very large (S 2 / S 1 >>1, the total absorption spectrum α when the lower absorber 32 fills the entire available surface area tot (λ) is shown.

[0066] S 2 / S 1 Very small total absorption spectrum α tot (λ) the quarter wave cavity C 1 The spectrum shows a peak at the anti-resonant wavelength of S, i.e., about 5 μm. 2 / S 1 The total absorption spectrum α is very large. tot (λ) the quarter wave cavity C 2 The spectrum shows a peak at the anti-resonant wavelength of S, i.e., approximately 3 μm. 2 / S 1 = 0.5 and S 2 / S 1 = 3 for the total absorption spectrum α tot These absorption limitations are not observed in (λ).

[0067] Figures 6A and 6B are partial schematic diagrams of a thermal detector 1 of electromagnetic radiation according to an 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 is configured to have more than two absorbers, in this case three separate quarter-wave cavities C for the absorption spectral bands. 1 , C 2 , C 3 The thermometer transducer 23 has the same thermometer transducer 23 thermally coupled to three absorbers 31, 32, 33 forming a

[0069] The absorbing film 20 here comprises a lower insulating layer 21, a thin metal film in two spatially distinct portions 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 in contact with 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 spaced a distance h from the reflector 12. 1 , located on the thermometer transducer 23. The quarter wave cavity C 1 Therefore, the spectral band Δλ 1 The wavelength λ c1 This allows optimizing the absorption by the upper absorber 31 at 1000 K. The medium includes in particular the upper protective layer 24, the thermistor material 23 and the two insulating layers 22, 21. As shown in Fig. 6C, the upper absorber 31 extends only over a 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 parts, which are polarized electrodes, is located at a distance h from the reflector 12. 2 A second absorber 32 (quarter wave cavity C 2) is formed. This quarter-wave cavity C 2 In the figure, 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 λ c2 Spectral subband Δλ centered at 2 This quarter-wave cavity C 2 The medium concerned here in particular comprises two insulating layers 21,22.

[0072] 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 covered 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 a third absorber 33. This is at the same distance h from the reflector 12 as the second absorber 32. 2 The absorption by the third absorber 33 is at a wavelength λ c3 Spectral subband Δλ centered at 3 This quarter-wave cavity C 3 The relevant medium here in particular comprises a top protective layer 24, a thermistor transducer 23 and two insulating layers 22,21.

[0073] Thus, three quarter-wave cavities C 1 , C 2 , C 3 is the height h 1 and h 2 (In this case, the distance h of the third absorber 3 h 2 ) and the equivalent refractive index n eq1 , n eq2 and n eq3 For the absorption value α above the reference value tot Broad detection spectral band while maintaining Δλ tot Thus, the quarter-wave cavity C 2 is a quarter wave cavity C 1The quarter-wave cavity C can be designed to absorb optimally at the anti-resonance of 3 For example, such a cavity, or a quarter-wave cavity C 3 By adjusting the thickness of such a layer of the absorbent membrane 20 disposed at 1 and Δλ 2 The spectral band Δλ included between 3 It can be designed to be absorbed within

[0074] Figure 7A is a partially 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 number of spatially distinct portions in the plane XY forming polarizing electrodes and a number 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 an opening 22a in contact with 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 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 are at a distance h from the reflector 12. 1These form a first absorber 31 spaced apart by . These are covered by the thermometer transducer 23 and are arranged in the spectral band Δλ 1 Resonant wavelength λ c1 Quarter-wave cavity C 1 Define the refractive index n eq1 The medium includes in particular a thermometer transducer 23 and two insulating layers 21,22.

[0079] The sides are at the same distance h from the reflector 12. 1 2, which is not covered by the thermometer transducer 23 and which is in the spectral band Δλ 5 Resonant wavelength λ c5 Quarter-wave cavity C 5 Define the refractive index n eq5 The medium in particular comprises two insulating layers 21,22.

[0080] The three other sides form different absorbents 32, 33, 34, which are spaced between themselves and have a value h 1 Different distance h 2 , h 3 and h 4 They are not covered by the thermometer transducer 23 and are spaced from the reflector 12 by a quarter wave cavity. c2 , C 3 and C 4 These 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 absorbent membrane has different levels at which the absorbers 32, 33, 34 are located. These are therefore connected to the main flat part on which the thermometer transducer 23 is located by a vertical (as shown) or inclined connection part, at a respective distance h 2 , h 3 and h 4Only at the axial end of the absorber 32, 33, 34 are there any flat portions at which the absorbers 32, 33, 34 are spaced apart from the reflector 12. The flat portions on which the absorbers 32, 33, 34 are arranged thus form steps of the absorbing film 20 relative to the main flat portion.

[0082] Thus, the resorbable membrane 20 has a height h 1 From 5 and the equivalent refractive index n eq1 From eq 5, the absorption value α above the reference value is uniform tot Broad detection spectral band while maintaining Δλ tot Multiple quarter-wave cavities can be designed to absorb optimally at the antiresonances of other quarter-wave cavities, which in turn can be designed to absorb in spectral bands that fall between those of the other quarter-wave cavities.

[0083] Although 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 Post 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 The third absorber 33.1 Part 33.2 Part 34 Absorber 35 Absorber

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 insulated from the readout substrate (10), the absorbent membrane (20) having a thermometer transducer (23) electrically connected to the readout circuitry; thermally coupled to the thermometer transducer (23); wavelength λ c1 The spectral band Δλ is centered on tot Spectral subbands Δλ 1 configured to absorb the electromagnetic radiation within the wavelength λ c1 First quarter-wave cavity for C 1 λ to form c1 / 4n eq1 A value equal to h 1 and is spaced from the reflector (12) by 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) having thermally coupled to the thermometer transducer (23); It is disposed on the absorbent membrane (20) so as not to be covered by the first absorbent body (31). Total surface area S 2 At least one second thin film absorber (32) having An absorbent membrane (20) having A thermal detector (1) having The second absorber (32) has a wavelength λ c2 The spectral band Δλ is centered on 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 to form c2 / 4n eq2 A value equal to h 2 and is spaced from the reflector (12) by 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 focus on and the first and second absorbents (31, 32) have a surface area ratio S 2 / S 1 is comprised between 0.5 and 3, Heat detector(1).

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

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

4. 4. A thermal detector (1) according to claim 3, wherein the second absorber (32) is formed by parts (32.1, 32.2) of a metal layer which on the one hand forms polarizing tracks at a holding arm (3) which ensures support and thermal insulation of the absorbent membrane (20) and, on the other hand, polarizing electrodes which are in contact with the thermometer transducer (23).

5. 5. The thermal detector (1) according to claim 4, wherein the metal layer extends planarly into the retaining arm (3) and into the absorbing membrane (20).

6. wavelength λ c3 The spectral band Δλ is centered on tot Spectral subbands Δλ 3 configured to absorb said electromagnetic radiation within a wavelength λ c3 Quarter-wave cavity for C 3 λ to form c3 / 4n eq3 A value equal to h 3 and is spaced from the reflector (12) by 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) between said first absorber and said second absorber.

7. distance h 3 is the distance h 2 7. The thermal detector (1) of claim 6, wherein said third absorber (33) is covered by said thermometer transducer (23).

8. wavelength λ c4 The spectral band Δλ is centered on tot Spectral subbands Δλ 4 configured to absorb said electromagnetic radiation within a wavelength λ c4 Quarter-wave cavity for C 4 λ to form c4 / 4n eq4 A value equal to h 4 and is spaced from the reflector (12) by n eq4 is the quarter wave cavity C 4 the refractive index of the medium related to 4 2. The thermal detector (1) according to claim 1, wherein the absorber is in a flat part of the absorbing film (20) which forms a step with respect to a main plane in which extends a metal layer which forms a polarizing electrode which is in contact with the polarizing track arranged on the holding arm (3) and the thermometer transducer (23).

9. The spectral band of detection 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.

10. The spectral band of detection 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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