DEVICE FOR IMPROVED MULTISPECTRAL DETECTION

Description

Domaine technique de l'invention

[0001] The invention relates to a multispectral detection device.

[0002] The invention also relates to a method for manufacturing a multispectral detection device. État de la technique

[0003] In the field of detection devices, in order to capture maximum information on a scene being observed, it is advantageous to use several different spectral bands.

[0004] Several detectors are used, each associated with different spectral bands. In this way, each detector captures specific information from the observed scene, facilitating analysis by combining the different data.

[0005] A simple way to create a detection device is to combine several different photodetectors, each configured to detect a specific spectral band. Each photodetector is paired with a readout circuit that stores the electrical charges representing the received information.

[0006] The generated electrical information is then sent to a processing circuit which analyzes the different data to provide information usable by the user.

[0007] Typically, the detection system comprises two photodetectors, each constructed using a specific architecture and semiconductor materials to detect radiation in a first spectral band. The system also includes two photodetectors, constructed using a different architecture. These second photodetectors are made from different semiconductor materials to detect radiation in a second spectral band.

[0008] Such an embodiment is complicated to implement because it requires two different stacks with different semiconductor materials to form two different types of photodetectors.

[0009] As an alternative, it is proposed to produce first and second photodetectors which are both sensitive to the first spectral band and the second spectral band.

[0010] To specialize the photodetectors to the first or second spectral band, filters are associated with each photodetector. First-order filters are placed only above the first photodetectors so as to allow only the first spectral band to pass through. Second-order filters are placed only above the second photodetectors so as to allow only the second spectral band to pass through. This teaching is described in document CN203883014.

[0011] However, it appears that such an embodiment is also very complicated to implement because it requires the creation of a first filter above the first photodetectors and the creation of a second filter above the second photodetectors. Il Therefore, the two filters must be implemented on the photodetector array.

[0012] A substantially equivalent teaching method is described in document US 2014 / 0034603. In this document, a multispectral filter is positioned above the photodetectors. This multispectral filter comprises several different filters, allowing different wavelengths to pass through and thus separating the incident radiation.

[0013] An alternative embodiment is described in US patent 7,109,488, which describes a multicolor infrared detection device. First and second pixels are defined in a photodetector array. These first and second pixels are defined by different first and second filters, which are associated with different photodetectors.

[0014] The first filter allows infrared radiation down to a wavelength of 9 microns to pass through. The photodetector is configured to detect radiation between 7 and 9 microns. The pixel will therefore deliver a signal representative of radiation between 7 and 9 microns.

[0015] The second filter allows infrared radiation to pass through up to a wavelength of 10 microns. The associated photodetector is configured to detect radiation between 7 and 9 microns and radiation between 9 and 10 microns. The second pixel will therefore deliver a signal representative of the radiation between 7 and 10 microns.

[0016] Another embodiment is described in document WO 2015 / 189423, which deals with bispectral array sensors. This document proposes using identical photodetectors to form a single-type array sensor. Here again, a complex filtering system allows the photodetectors to be specialized so that some of them observe one spectral band and others observe a different spectral band.

[0017] All photodetectors are covered by a dual-band interference filter which is configured to allow the passage of radiation from a first spectral band and a second spectral band.

[0018] Part of these photodetectors is covered by a low-pass filter to receive only radiation from the first spectral band. The other part of these photodetectors is covered by a high-pass filter to receive only radiation from the second spectral band.

[0019] It appears that this solution is particularly complex to implement and expensive.

[0020] US patent 2013 / 0188057 discloses an image capture device configured to separate multiple colors in the visible spectrum and which includes a filter blocking infrared radiation. EP2117047 discloses a visible radiation capture device equipped with color filters and a white filter for signal separation. Applicant's EP2827375 discloses an infrared detection device mounted on a cooler and associated with a cold screen surmounted by a lens.

[0021] US patent 2016 / 080669 discloses a visible light sensor with filters of different colors. The assembly is topped by an infrared filter covering all the photosensitive elements. EP2442555 discloses an image sensor equipped with an optical filter defining two transmission bands.

[0022] US patent 2005 / 0189492 discloses an infrared detection device having a two-pixel array associated with a two-filter array to detect two distinct wavelength ranges. The filter array is formed on a substrate that is aligned with the pixel array so that the first pixel receives a different signal than the second pixel. Objet de l'invention

[0023] The invention aims to provide a multispectral detection device that can be made more easily and can be more compact.

[0024] This result is to be achieved by means of a device according to claim 1, i.e., by means of a multispectral detection device which comprises, among other things: a first photodetector and a second photodetector, each sensitive to a first wavelength range and a second wavelength range different from the first wavelength range, the first photodetector delivering a first signal representative of the received radiation and the second photodetector delivering a second signal representative of the received radiation, a first filter configured to allow the first wavelength range to pass through and to block the second wavelength range, the first filter covering the first photodetector and leaving the second photodetector exposed, the first filter being in contact with the first photodetector so as to block the passage of the second wavelength range into the first photodetector, a second filter disposed at a distance from the first and second photodetectors and at a distance from the first filter,the second filter being configured to allow the first wavelength range and the second wavelength range to pass through, the second filter being configured to block a wavelength greater than the longest of the wavelengths among the first and second wavelength ranges and / or to block a wavelength shorter than the shortest of the wavelengths among the first and second wavelength ranges.

[0025] In one development, the second photodetector is without a filter configured to block the first wavelength range so as to receive the first and second wavelength ranges, the detection device having a processing circuit configured to receive electrical signals from the first and second photodetectors and provide information about the radiation of the second wavelength range by comparison of the first signal with the second signal.

[0026] Alternatively, the second photodetector is covered by a third filter configured to block the first wavelength range and allow the second wavelength range to pass through.

[0027] In an advantageous embodiment, the second filter is chosen from among the low-pass, high-pass, band-pass and dual-band filters.

[0028] Preferably, the first filter is a low-pass, high-pass, or band-pass filter that cuts off the second wavelength range.

[0029] Il It is interesting to plan for the second filter to be placed at a distance from the first filter and the second photodetector by a layer of gas or a vacuum.

[0030] In one embodiment, the detection device includes a cold screen configured to focus the incident radiation by means of a radiation passage orifice, and the second filter is disposed in said orifice.

[0031] Preferably, the cold screen defines a closed enclosure containing the first and second photodetectors, and the second filter is disposed in the closed enclosure.

[0032] Alternatively, the cold screen defines a closed enclosure containing the first and second photodetectors, and the second filter is placed outside the closed enclosure.

[0033] The invention also aims to provide a simpler method for manufacturing a multispectral detection device.

[0034] This result is to be achieved by means of a manufacturing process according to claim 10, i.e. by means of a manufacturing process for a multispectral detection device which includes, among other things, the following steps: provide a substrate comprising first and second photodetectors, each sensitive to a first wavelength range and a second wavelength range different from the first wavelength range, the first photodetector delivering a first signal representative of the received radiation and the second photodetector delivering a second signal representative of the received radiation; form a first filter configured to allow the first wavelength range to pass through and to block the second wavelength range, the first filter covering the first photodetector and leaving the second photodetector exposed, the first filter being in contact with the first photodetector so as to block the passage of the second wavelength range into the first photodetector; form a second filter disposed at a distance from the first and second photodetectors and at a distance from the first filter.the second filter being configured to allow the first wavelength range and the second wavelength range to pass through, the second filter being configured to block a wavelength longer than the longest wavelength among the first and second wavelength ranges and / or to block a wavelength shorter than the shortest wavelength among the first and second wavelength ranges.

[0035] In a particular development, the process includes, before forming the second filter: form a third filter configured to allow the second wavelength range to pass through and to block the first wavelength range, the third filter covering the second photodetector and leaving the first photodetector uncovered, the third filter being in contact with the second photodetector so as to block the passage of the first wavelength range into the second photodetector. Description sommaire des dessins

[0036] Other advantages and features will become clearer from the following description of particular embodiments of the invention given by way of non-limiting examples and shown in the accompanying drawings, in which: THE figures 1 And 2 schematically represent two alternative embodiments of a detection device equipped with two photodetectors and a filter on the cold screen, figures 3a-3f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a first embodiment, the figures 4a-4f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a second embodiment, the figures 5a-5f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a third embodiment, the figures 6a-6f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a fourth embodiment, the figures 7a-7f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a fifth embodiment, the figures 8a-8f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a sixth embodiment, the figures 9a-9f represent, schematically, the intensity, transmittance and absorbance curves of the different components of the detection device according to a seventh embodiment, the figure 10 represents, schematically, another embodiment of a detection device equipped with two photodetectors and a filter on the cold screen. Description détaillée

[0037] THE figures 1 And 2illustrate a multispectral detection device which includes at least a first photodetector 1a sensitive to a first range of wavelengths also called the first spectral band and a second photodetector 1b sensitive to a second range of wavelengths also called the second spectral band.

[0038] In one particular embodiment, the first photodetector 1a and the second photodetector 1b comprise a single semiconductor film configured to absorb the first and second wavelength ranges. This embodiment is particularly advantageous because it is very compact.

[0039] In one embodiment, the first photodetector 1a and the second photodetector 1b each comprise separate first and second semiconductor films which are respectively configured to capture the first wavelength range and the second wavelength range.

[0040] These two embodiments are advantageous because the two photodetectors can be made simultaneously, which facilitates the manufacturing process and the integration density.

[0041] In an advantageous embodiment, the multispectral detection device comprises a plurality of first photodetectors and a plurality of second photodetectors. Advantageously, the first and second photodetectors form an array. Il It is particularly advantageous to ensure that the first and second photodetectors are evenly distributed over the detection surface.

[0042] In an advantageous embodiment, the plurality of first photodetectors and the plurality of second photodetectors form a focal plane array, that is to say that all the photodetectors are made in the same plane.

[0043] Preferably, the detection system comprises an equal number of first and second photodetectors. Alternatively, it is also possible to designate the detection system to have a different number of first and second photodetectors than the number of second photodetectors.

[0044] In one particular embodiment, the second wavelength range differs from the first wavelength range. Advantageously, the second wavelength range is separate from the first wavelength range; that is, the wavelength ranges do not overlap. Depending on the embodiment, the first and second wavelength ranges either share a common boundary or are separated by an intermediate wavelength range.

[0045] The first photodetector 1a and the second photodetector 1b are both sensitive to the first and second wavelength ranges. In other words, the first photodetector 1a and the second photodetector 1b are capable of detecting radiation emitted in the first wavelength range and providing an electrical signal representative of this radiation. The first photodetector 1a and the second photodetector 1b are also capable of detecting radiation emitted in the second wavelength range and providing an electrical signal representative of this radiation.

[0046] It is also possible that the first photodetector 1a and the second photodetector 1b are capable of capturing radiation emitted in a third wavelength range that differs from the first and second wavelength ranges. This third wavelength range does not contain relevant information, but it simplifies the fabrication of the photodetectors by allowing the use of more readily available semiconductor materials.

[0047] The first and second wavelength ranges are ranges of infrared radiation. In a particular embodiment, the first and second wavelength ranges are chosen from the following ranges: NIR: between 0.8µm and 1.4µm SWIR: between 1.4µm and 3µm, MWIR: between 3µm and 8µm, LWIR: between 8µm and 15µm.

[0048] It is therefore possible to configure the detection device so that it can detect different pairs of wavelength ranges, for example MWIR / LWIR, MWIR / SWIR, LWIR / SWIR, NIR / SWIR, NIR / LWIR or NIR / MWIR.

[0049] It is still possible to divide the different wavelength ranges presented above into two different sub-ranges. In one particular embodiment, the first and second wavelength ranges, for example, divide MWIR radiation into two distinct sub-ranges. The same can be true for LWIR, SWIR, or NIR radiation.

[0050] The first and second photodetectors 1a and 1b can be formed from any suitable detector type, for example, a photodiode, a quantum well detector, or a multi-quantum well detector. Other types of photodetectors are also possible. The first and second photodetectors 1a and 1b can be implemented in identical or different architectures. Advantageously, the first photodetector 1a is identical to the second photodetector 1b, i.e., in terms of materials and implementation architecture. This makes it much easier to implement the photodetectors in a compact manner.

[0051] The power supply conditions for photodetectors 1a and 1b may differ. Advantageously, the power supply conditions are identical for all photodetectors. The power supply conditions are provided by a first readout circuit 2a for the first photodetector 1a and by a second readout circuit 2b for the second photodetector 1b.

[0052] The photodetectors 1a and 1b and the reading circuits 2a and 2b are advantageously arranged on a support 3.

[0053] To specialize the first and second photodetectors 1a and 1b, the photodetectors are connected to an incident radiation filtering system 4. This filtering system is configured so that the first photodetector 1a receives different radiation than the second photodetector 1b. In this way, the two photodetectors 1a and 1b are able to provide two different pieces of information about the observed scene.

[0054] As mentioned above, using identical photodetectors makes it easier to create a compact device. However, the compactness is such that it becomes difficult to create different and efficient filters above the first photodetector 1a and above the second photodetector 1b.

[0055] To facilitate the implementation of a high-performance detection device, the filtering system 4 is a separate filtering system, meaning that it comprises at least a first filter 4a and a second filter 4b with different optical properties, arranged successively in the optical path of the first photodetector 1a. The first filter 4a and the second filter 4b are not in contact with each other, which simplifies the implementation of the filtering system 4. The first filter 4a has optical and preferably mechanical characteristics different from those of the second filter 4b.

[0056] The use of two separate and consecutive filters in the optical path makes it possible to reduce the thickness of the filter placed in contact with the photodetector compared to an equivalent filter which is also in contact with the photodetector.

[0057] Typically, the thickness of a filter is approximately equal to the wavelength of the cutoff frequency. Thus, for a photodetector configured to absorb radiation in the 3-5µm range, the equivalent filter has a thickness approximately between 3µm and 5µm.

[0058] It is clear that such a thickness poses a manufacturing problem for photodetector arrays with a repetition rate of less than 30 µm. The integration problem is even more critical for photodetector arrays with a repetition rate of less than 20 µm. Significant manufacturing problems are present for photodetector arrays with a repetition rate of less than 15 µm, particularly when the filter has a thickness of 5 µm.

[0059] It also appears that to improve filter performance, and in particular to increase its ability to effectively block a portion of the incident radiation, the number of layers forming the filter must be increased, which increases the filter's thickness. For example, to increase the filter's rejection power—that is, its ability to block incident radiation—by 10% compared to a reference filter, the thickness must be increased by approximately 2 µm.

[0060] It also appears that for detection devices operating at low temperatures, typically below 0°C, the filter introduces significant thermomechanical stresses in the photodetector, degrading the device's performance. These thermomechanical stresses increase with increasing thickness.

[0061] The filtering system 4 includes a first filter 4a which is configured to allow the first wavelength range to pass through and to block the second wavelength range. The first filter 4a can be an interference filter or an absorption filter.

[0062] Depending on the embodiment, the first wavelength range may have longer or shorter wavelengths than the second wavelength range. The first filter 4a can therefore be a low-pass or high-pass filter whose cutoff wavelength lies between the first and second wavelength ranges. This embodiment is particularly advantageous because low-pass and high-pass filters are easy to manufacture, simplifying their integration onto the surface of the photodetectors. They are generally thinner than other filters.

[0063] Alternatively, it is also possible to designate the first filter 4a as a bandpass filter that allows the first wavelength range to pass through while blocking the second wavelength range. This embodiment is slightly less advantageous than the previous one because a bandpass filter is generally thicker than a low-pass or high-pass filter.

[0064] The first filter 4a is deposited directly onto the first photodetector 1a, that is, onto a portion of the focal plane grating. The first filter 4a is not deposited on the second photodetector 1b; thus, the first filter 4a covers the first photodetector 1a, leaving the second photodetector 1b uncovered. The first filter 4a is in physical contact with the first photodetector 1a. The first filter 4a limits crosstalk between the first photodetector 1a and the adjacent second photodetector 1b.

[0065] With this particular configuration, the first photodetector 1a receives only a portion of the incident radiation. The first photodetector 1a receives the first wavelength range and not the second wavelength range.

[0066] To effectively eliminate stray radiation, the filtering system 4 also includes a second filter 4b. This second filter 4b is used to block some of the incident radiation before it is captured by the first and second photodetectors 1a and 1b. More precisely, the second filter 4b is used to block some of the incident radiation before it reaches the focal plane and, in particular, the first filter 4a, which blocks another portion of the incident radiation.

[0067] The second filter 4b is positioned at a distance from the first photodetector 1a and the second photodetector 1b, that is to say that the second filter 4b is not in direct contact with the first photodetector 1a, nor with the second photodetector 1b.

[0068] The second 4b filter is deposited on a second substrate which is different from the first substrate supporting the first and second photodetectors or on which the first and second photodetectors are formed.

[0069] Depending on the embodiment, the second filter 4b can be an interference filter or an absorption filter.

[0070] The first filter 4a and the second filter 4b work together to filter the radiation received by the first photodetector 1a.

[0071] By separating the first filter 4a and the second filter 4b, it is possible to obtain a single filter capable of allowing only the relevant radiation to pass through towards the first photodetector, while limiting the thickness of the first filter 4a formed directly on the first photodetector. In this way, it is possible to create more compact first filters.

[0072] The second filter 4b is separated from the photodetectors 1a and 1b and from the first filter 4a by a layer of gas or vacuum. This significantly reduces, or even eliminates, the thermomechanical stresses associated with the second filter 4b. This makes it easier to form the first filter 4a and the second filter 4b. The thickness of the first filter can also be reduced, further decreasing the thermomechanical stresses.

[0073] In a particular embodiment, the second filter 4b is advantageously transferred to the substrate containing the first photodetector 1a and the second photodetector 1b. The second filter 4b can then be formed separately from the first filter 4a, and the process of manufacturing the second filter 4b does not interfere with the first filter 4a, nor with the photodetectors 1a and 1b.

[0074] In an alternative embodiment, the second filter 4b is advantageously transferred to the support 3, which is configured to support the substrate containing the first photodetector 1a and the second photodetector 1b. Here again, the second filter 4b can then be formed separately from the first filter 4a, and the manufacturing process of the second filter 4b does not interfere with the first filter 4a, nor with the photodetectors 1a and 1b.

[0075] The second filter 4b is positioned at a distance from the first filter 4a and the photodetectors 1a and 1b. This second filter 4b is a common filter for both the first photodetector 1a and the second photodetector 1b. In this way, the second filter 4b is not subject to alignment constraints with respect to the first filter 4a or the second photodetector 1b. The second filter 4b is located between the radiation source and the first filter 4a, as well as between the radiation source and the second photodetector 1b. Because the second filter 4b is positioned at a distance from the first filter 4a and the photodetectors, manufacturing and integration constraints are reduced compared to prior art devices.

[0076] The second 4b filter is configured to allow the first and second wavelength ranges to pass through. The second 4b filter is advantageously configured to block the third wavelength range, which differs from the first and second wavelength ranges.

[0077] Advantageously, the second 4b filter is a band-stop filter. It is also possible to create a low-pass, high-pass, or bi-lobe filter.

[0078] Depending on the embodiment, and without being exhaustive, the second filter 4b can be configured to block wavelengths outside the following ranges: 0.8µm - 3µm, for capturing NIR and SWIR radiation, 1.4µm - 8µm, for capturing SWIR and MWIR radiation, 3µm - 15µm, for capturing MWIR and LWIR radiation, 0.8µm - 1.4µm, for capturing NIR radiation, 1.4µm - 3µm, for capturing SWIR radiation, 3µm - 8µm, for capturing MWIR radiation, 8µm - 15µm, for capturing LWIR radiation

[0079] In this way, the filtering system 4 prevents certain wavelengths from reaching the first and second photodetectors 1a / 1b and polluting the useful signals received.

[0080] In one particular embodiment, the second photodetector 1b has no filter in direct contact with its surface. In this configuration, the second photodetector 1b receives both the first and second wavelengths because it is not associated with the first filter 4a. This embodiment is particularly advantageous because only the first photodetector 1a is covered by a first filter 4a, which simplifies the construction of the detection device with small photodetectors.

[0081] The first photodetector 1a emits an electrical signal that is representative of the received radiation. The electrical signal from the first photodetector 1a is representative of the radiation in the first wavelength range only.

[0082] The second photodetector 1b also emits an electrical signal that is representative of the received radiation. The electrical signal from the second photodetector 1b is representative of the radiation in the first wavelength range and in the second wavelength range.

[0083] In order to obtain a signal representative of the radiation in the second wavelength range, it is advantageous to compare the electrical signal from the first photodetector 1a with the electrical signal from the second photodetector 1b.

[0084] The differences in information between the two signals are representative of the radiation in the second wavelength range.

[0085] Advantageously, the first photodetector 1a is connected to a readout / processing circuit 5 that receives the first electrical signal. The second photodetector 1b is also connected to the readout / processing circuit 5, which receives the second electrical signal. The readout / processing circuit 5 is configured to compare the first electrical signal with the second electrical signal and to provide a third signal representative of the radiation received by the second photodetector 1b in the second wavelength range. In one embodiment, the readout / processing circuit can be implemented in the substrate 3. Alternatively, the readout and processing functions can be separated, with the readout function implemented in the substrate 3 and the processing function implemented separately.

[0086] It is advantageous to use a second 4b filter, which is either a high-pass or low-pass filter. The second 4b filter is then configured to allow the first and second wavelength ranges to pass through, and to block a wavelength greater than the largest of the first and second wavelength ranges, or to block a wavelength less than the smallest of the first and second wavelength ranges.

[0087] It is also advantageous to use a second 4b filter whose cutoff wavelength corresponds to one end of the range formed by the first and second wavelength ranges. In this way, some of the manufacturing uncertainties of the photodetectors are eliminated.

[0088] It is particularly advantageous to use a second 4b filter, which is a bandpass filter whose lower and upper cutoff wavelengths correspond to the extremes of the interval defined by the first and second wavelength ranges. In this way, some of the manufacturing uncertainties of the photodetectors are eliminated.

[0089] Alternatively, the second filter, 4b, can be a bi-lobe filter, also called a dual-band filter, which is more complex to manufacture and thicker. The bi-lobe filter is configured to allow the first wavelength range to pass through, and the second wavelength range to pass through. This filter allows for better selection of useful wavelengths. Its greater complexity and thickness are no longer problems because the filter is offset from the photodetectors.

[0090] The second filter 4b allows the first wavelength range and the second wavelength range to pass through and excludes, at least partially or even totally, radiation in the unwanted wavelength ranges.

[0091] The inventors observed that this embodiment is particularly advantageous compared to prior art designs. Indeed, prior art documents propose to implement a first filter on the first photodetector and a second, different filter on the second photodetector.

[0092] The two filters used have substantial thicknesses, which can be of the same order of magnitude as the lateral dimension of the photodetector. It is therefore difficult to accurately control the design of a detection array with a small spacing between the photodetectors.

[0093] By using a single filter, here the first filter 4a, to specialize the first photodetectors relative to the second photodetectors, it is easier to create a detection array with a small repetition rate. Alignment constraints are limited to the first filter 4a in the manufacturing process.

[0094] Using a single first 4a filter, configured to allow the first wavelength range to pass through while blocking the second, has the advantage of being simple to implement. It eliminates the constraints associated with subsequent deposition and etching or lift-off steps to form another filter on the substrate containing the photodetectors. The first 4a filter can be a thin filter, and the technological steps required to form this first filter are reduced, thus minimizing the risk of damage to the first and / or second photodetectors.

[0095] It is particularly advantageous to choose the low-pass, high-pass or band-pass filter that is easiest to make and / or the thinnest in order to block part of the incident radiation and thus specialize the first photodetector 1a in relation to the second photodetector 1b.

[0096] In one particular embodiment, an anti-reflective layer (not shown) is used. Depending on the embodiment, the anti-reflective layer can be placed on the second filter 4b, meaning that the second filter 4b separates the anti-reflective layer from the photodetectors 1a and 1b. Alternatively, the anti-reflective layer is deposited on the second photodetector 1b and on the first filter 4a. The anti-reflective layer separates the second filter 4b and the first filter 4a. Advantageously, a first anti-reflective layer is deposited on the photodetectors 1a and 1b, and a second anti-reflective layer is deposited on the second filter 4b or in contact with the second filter 4b. Depending on the embodiment, the anti-reflective layer can be deposited on the first filter or between the first photodetector 1a and the first filter 4a. The anti-reflective layer is advantageously configured to allow infrared radiation to pass through.

[0097] A passivation layer is used to cover the first and / or second photodetectors 1a and 1b. This layer is positioned between the first photodetector 1a and the first filter 4a. The passivation layer has a thickness ranging from 10 nm to 2000 nm. Using a passivation layer is particularly advantageous for limiting contamination of the unfiltered band. For example, contamination of the unfiltered band can result from external elements or the diffusion of contaminants. The passivation layer keeps contaminants away from the photodetectors and / or filters to prevent any alteration of optical and / or electrical performance. Examples of contaminants include gold and copper.

[0098] The detection system includes a continuous passivation layer that monolithically covers the first and second photodetectors 1a and 1b. This continuous passivation layer improves thermomechanical stress management by smoothing the stresses on the first and second photodetectors. It is particularly advantageous to use a material with a low diffusion coefficient for contaminant species for this passivation layer.

[0099] In a particular embodiment, an adhesion promoter is disposed between the photodetectors and / or filters and the passivation layer.

[0100] In one particular embodiment, the passivation layer is made of a material chosen from Ge, ZnS, CdTe, SiO₂, or SiN₂ so as to simultaneously form a passivation layer and an antireflective layer. The antireflective layer can consist of a single layer in a single material or a stack of several layers in different materials.

[0101] The inventors also observed that it is advantageous to use first and second photodetectors that are sensitive to the first wavelength range, to the second wavelength range, and not sensitive between these two wavelength ranges. Thus, the specialization of the first photodetector 1a with respect to the second photodetector 1b is easily achieved because the constraint on the cutoff frequency of the first filter 4a is reduced.

[0102] This embodiment is also advantageous because the constraints on the second 4b filter are also reduced.

[0103] However, in many cases, photodetectors are sensitive to at least a third wavelength range located between the first and second wavelength ranges. In such cases, using a bi-lobe filter is advantageous.

[0104] It appears that using a photodetector with a sensitivity that extends beyond the first wavelength range and beyond the second wavelength range allows for the relaxation of certain technological constraints that are linked to the manufacturing processes of the photodetectors and / or the materials used.

[0105] However, using photodetectors sensitive outside the first wavelength range and outside the second wavelength range results in the addition of spurious signals from unwanted radiation ranges.

[0106] Filtering system 4 is configured to block this third wavelength range. More specifically, the third wavelength range is blocked by the second filter, 4b.

[0107] In a particularly advantageous embodiment, illustrated by the transmission curves of figures 3b And 4bThe second filter, 4b, is a high-pass filter configured to cut off wavelengths below the lower end of the range defined by the first and second wavelength ranges. This filter blocks stray radiation corresponding to wavelengths shorter than the cutoff wavelength, which can be absorbed by photodetectors 1a and 1b.

[0108] In this scenario, the first filter 4a can be a high-pass filter, a low-pass filter, or a band-pass filter.

[0109] If the first filter 4a is a low-pass filter whose transmission curve is illustrated in the figure 3c The first wavelength range has shorter wavelengths than the second wavelength range. The first photodetector 1a only receives the wavelength range associated with the shorter wavelengths, as illustrated by the intensity curve of the figure 3e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 3f . There figure 3d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0110] If the first filter 4a is a high-pass filter whose transmission curve is illustrated in the figure 4c The first wavelength range has longer wavelengths than the second wavelength range. The first photodetector 1a only receives the wavelength range associated with the longer wavelengths, as illustrated by the intensity curve of the figure 4e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 4f . There figure 4d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0111] If the first filter 4a is a bandpass filter (not shown), the first wavelength range may have shorter or longer wavelengths than the second wavelength range, depending on the characteristics of the first filter 4a. If the first filter 4a is configured to allow the shorter wavelengths to pass through, then its operation is equivalent to a low-pass filter. If the first filter 4a is configured to allow the longer wavelengths to pass through, then its operation is equivalent to a high-pass filter.

[0112] In another embodiment illustrated by the transmission curves of figures 5b And 6bThe second filter 4b is a low-pass filter configured to cut off wavelengths above the upper end of the interval defined by the first and second wavelength ranges. Such a filter blocks stray radiation corresponding to wavelengths above the cutoff wavelength, which can be absorbed by photodetectors 1a and 1b ( figure 5d ).

[0113] In this scenario, the first filter 4a can be a high-pass filter, a low-pass filter, or a band-pass filter.

[0114] If the first filter 4a is a low-pass filter whose transmission curve is illustrated in the figure 5c The first wavelength range has shorter wavelengths than the second wavelength range. The first photodetector 1a only receives the wavelength range associated with the shorter wavelengths, as illustrated by the intensity curve of the figure 5e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 5f . There figure 5d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0115] If the first filter 4a is a high-pass filter whose transmission curve is illustrated in the figure 6c The first wavelength range has longer wavelengths than the second wavelength range. The first photodetector 1a only receives the wavelength range associated with the longer wavelengths, as illustrated by the intensity curve of the figure 6e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 6f . There figure 6d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0116] If the first filter 4a is a bandpass filter (not shown), the first wavelength range may have shorter or longer wavelengths than the second wavelength range, depending on the characteristics of the first filter 4a. If the first filter 4a is configured to allow the shorter wavelengths to pass through, then its operation is equivalent to a low-pass filter. If the first filter 4a is configured to allow the longer wavelengths to pass through, then its operation is equivalent to a high-pass filter.

[0117] In a particularly advantageous embodiment illustrated by the transmission curve of the figure 7b The second filter 4b is a bandpass filter configured to cut off wavelengths below the lower end of the interval defined by the first and second wavelength ranges and to cut off wavelengths above the upper end of the interval defined by the first and second wavelength ranges. Such a filter blocks stray radiation corresponding to wavelengths below and above the two cutoff wavelengths, which can be absorbed by photodetectors 1a and 1b ( figure 7d ).

[0118] In this scenario, the first filter 4a can be a high-pass filter, a low-pass filter, or a band-pass filter.

[0119] If the first filter 4a is a high-pass filter whose transmission curve is illustrated in the figure 7c The first wavelength range has longer wavelengths than the second wavelength range. The first photodetector 1a only receives the wavelength range associated with the longer wavelengths, as illustrated by the intensity curve of the figure 7e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 7f . There figure 7d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0120] If the first filter 4a is a low-pass filter (not shown), the first wavelength range has shorter wavelengths than the second wavelength range. The first photodetector 1a receives only the wavelength range associated with the shorter wavelengths. The second photodetector 1b receives both wavelength ranges.

[0121] If the first filter 4a is a bandpass filter (not shown), the first wavelength range may have shorter or longer wavelengths than the second wavelength range, depending on the characteristics of the first filter 4a. If the first filter 4a is configured to allow the shorter wavelengths to pass through, then its operation is equivalent to a low-pass filter. If the first filter 4a is configured to allow the longer wavelengths to pass through, then its operation is equivalent to a high-pass filter.

[0122] In an embodiment illustrated in figures 8a à 8f The second filter, 4b, is a bi-lobe filter whose transmission curve is illustrated in the figure 8b The bi-lobe filter is associated with a first 4a high-pass filter whose transmission curve is illustrated in the figure 8c The first photodetector 1a receives only the wavelength range associated with the longest wavelengths, as illustrated by the intensity curve of the figure 8e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 8f . There figure 8d represents the absorption wavelength range of the first and second photodetectors 1a and 1b.

[0123] As with the other embodiments, the first filter 4a can be replaced by a bandpass filter or by a lowpass filter, which is illustrated by the figures 9a à 9f .

[0124] THE figures 3a , 4a , 5a 6a , 7a , 8a And 9a represent the light intensity of the observed scene.

[0125] The transmission curve of the low-pass filter is illustrated in the figure 9c The first photodetector 1a receives only the wavelength range associated with the shortest wavelengths, as illustrated by the intensity curve of the figure 9e The second photodetector 1b receives both wavelength ranges as illustrated by the intensity curve of the figure 9f . There figure 9d represents the range of wavelengths absorbed by the first and second photodetectors 1a and 1b.

[0126] In an alternative embodiment illustrated in the figure 10 The second photodetector 1b is covered by a third filter 4c. The third filter 4c is configured to allow the second wavelength range to pass through and block the first wavelength range. The third filter 4c can be an interference filter or an absorption filter.

[0127] The third filter, 4c, can be either a low-pass or a high-pass filter whose cutoff wavelength lies between the first and second wavelength ranges. If the first filter is a low-pass filter, the second filter is a high-pass filter, and vice versa.

[0128] Alternatively, the third filter, 4c, can be a bandpass filter that allows the second wavelength range to pass through while blocking the first. This embodiment is less advantageous than the previous one because a bandpass filter is thicker than a low-pass or high-pass filter.

[0129] The third filter 4c is deposited directly onto the second photodetector 1b, that is, onto a portion of the focal plane grating. The third filter 4c is not deposited on the first photodetector 1a; thus, it only covers the second photodetector 1b, leaving the first photodetector 1a uncovered. The third filter 4c is in physical contact with the second photodetector. The third filter 4c limits crosstalk between the first photodetector 1a and the adjacent second photodetector 1b.

[0130] With this particular configuration, the second photodetector 1b receives only a portion of the incident radiation. It receives the second wavelength range and not the first. Each photodetector provides information representative of the observed wavelength range. The processing circuit can be simplified because it is no longer necessary to compare the signals from the two photodetectors.

[0131] In the various examples illustrated in figures 3a , 4a , 5a , 6a , 7a , 8a And 9a , the emission curve of the observed scene extends beyond the first and second wavelength ranges.

[0132] The detection device can be simply implemented as follows. The first photodetector 1a and the second photodetector 1b are formed on a semiconductor substrate. Since both photodetectors 1a and 1b are sensitive to the same wavelength ranges, it is advantageous to fabricate both photodetectors simultaneously and with the same semiconductor materials. In a preferred embodiment, photodetectors 1a and 1b are identical.

[0133] The two photodetectors are offset along an axis parallel to the plane of the substrate surface and they are in the same plane which is parallel to the plane of the substrate surface.

[0134] A first filter 4a is formed on the first photodetector 1a so as to cover the first photodetector 1a and to leave the second photodetector 1b uncovered.

[0135] In a first embodiment, the first filter 4a is formed on the first photodetector 1a and on the second photodetector 1b. The first filter 4a is then removed above the second photodetector 1b.

[0136] In a second embodiment, the second photodetector 1b is protected by a sacrificial layer. The first filter 4a is formed on the first photodetector 1a and on the sacrificial layer. The sacrificial layer is removed to free the second photodetector 1b, which is now without the first filter.

[0137] Next, the second filter 4b is associated, for example brought into contact, with the substrate containing the first photodetector 1a and the second photodetector 1b. The second filter 4b is not formed by deposition on the substrate; it was formed independently and is subsequently added.

[0138] In the embodiment using the third filter 4c, the first filter 4a can be formed before or after the third filter 4c. It is also possible to have the first filter 4a and the third filter 4c formed partially simultaneously by sharing some layers. Advantageously, the third filter 4c is formed before the second filter 4b is installed. The third filter 4c is positioned at a distance from the second filter 4b.

[0139] As an example, it is advantageous to place the first and second photodetectors 1a and 1b in a closed enclosure that is advantageously airtight. This closed enclosure has an orifice configured to allow radiation to pass from the radiation source to the first and second photodetectors 1a and 1b. It is particularly advantageous to place the second filter 4b in this orifice so as to allow the first and second wavelength ranges to pass through and to block some of the unwanted radiation. The orifice is advantageously a window 6 made of transparent material covered by the second filter 4b. The second filter 4b can be located inside the closed enclosure ( figure 1 ) or outside the enclosed area ( figure 2 ). The entire surface of the window is advantageously covered by the second filter 4b in order to leave only the useful signal in all areas of the window.

[0140] Advantageously, the detection device is a cooled detection device, that is, a device that is configured to operate at a temperature below 300K, preferably between 40K and 300K and preferably below 200K. The detection device can also be uncooled.

[0141] The detection device is advantageously coupled with a cooling system 7 which allows it to be cooled to its operating temperature.

[0142] The photodetectors of the detection device can be made of II-VI material, for example HgCdTe or of III-V material, for example InGaAs, InSb, InAsSb.

[0143] Photodetectors 1a and 1b are advantageously surrounded by a cold screen 8, which is configured to block incident radiation except for the incident radiation passage window 6. It appears particularly advantageous to place the second filter 4b over this incident radiation passage window 6.

[0144] The areas covered by the first filter 4a and the areas left uncovered by the first filter 4a advantageously define an alternation between the first photodetectors 1a and the second photodetectors 1b.

[0145] This alternation between the first and second photodetectors can result in the creation of a checkerboard pattern or an alternation of bands represented by rows or columns of photodetectors.

[0146] In a preferred embodiment, the pressure inside the cold screen 8 is less than or equal to the pressure outside the cold screen 8. It is advantageous to provide that the pressure inside the cold screen 8 is less than atmospheric pressure, for example less than 1013 hPa.

[0147] In a particular embodiment, the pressure inside the cold screen is less than 10⁻⁴ Pa.

Claims

1. Multispectral detection device comprising: - a first photodetector (1a) and a second photodetector (1b) each sensitive to a first wavelength range and to a second wavelength range different from the first wavelength range, the first photodetector (1a) delivering a first signal representative of the received radiation and the second photodetector (1b) delivering a second signal representative of the received radiation, - a first filter (4a) configured for to allow the first wavelength range to pass and to block the second wavelength range, the first filter (4a) covering the first photodetector (1a) and leaving the second photodetector (1b) uncovered, the first filter (4a) being arranged on the first photodetector (1a) so as to block the passage of the second wavelength range in the first photodetector (1a) and generate thermomechanical stresses in the first photodetector (1a) and in the second photodetector (1b), - a second filter (4b) arranged at a distance from the first and second photodetectors (1a, 1b) and at a distance from the first filter (4a), the second filter (4b) being configured to allow the first wavelength range and the second wavelength range to pass, the second filter (4b) being configured to block a higher wavelength than the longest of the wavelengths in the first and second wavelength ranges and / or to block a lower wavelength than the shortest of the wavelengths in the first and second wavelength ranges, the first filter (4a) and the second filter (4b) being arranged successively in the optical path of the first photodetector (1a), the second filter (4b) being common to the first photodetector (1a) and the second photodetector (1b), the multispectral detection device being characterized in that the first and second wavelength ranges are infrared radiation ranges and in that it comprises: - a continuous passivation layer which monolithically covers the first and second photodetectors (1a, 1b) and is arranged between the first photodetector (1a) and the first filter (4a), the passivation layer having a thickness of between 10nm and 2000nm to smooth thermomechanical stresses on the first and second photodetectors (1a, 1b).

2. Detection device according to claim 1 wherein the second photodetector (1b) is devoid of a filter configured to block the first wavelength range so as to receive the first wavelength range and the second wavelength range, the detection device comprising a processing circuit (5) configured to receive electric signals coming from the first and second photodetectors (1a, 1b) and to provide data relative to the radiation of the second wavelength range by comparing the first signal with the second signal.

3. Detection device according to claim 1 wherein the second photodetector (1b) is covered by a third filter (4c) configured to block the first wavelength range and to allow the second wavelength range to pass.

4. Detection device according to any one of the foregoing claims characterised in that the second filter (4b) is chosen from low-pass, high-pass, bandpass and dual-band filters.

5. Detection device according to any one of the foregoing claims characterised in that the first filter (4a) is a low-pass, high-pass or bandpass filter cutting off the second wavelength range.

6. Detection device according to any one of the foregoing claims characterised in that the second filter (4b) is arranged at a distance from the first filter (4a) and the second photodetector (1b) separated by a layer of gas or a void.

7. Detection device according to any one of the foregoing claims characterised in that it comprises a cold shield (8) configured to focus the incident radiation by means of an aperture for passage of the radiation and in that the second filter (4b) is arranged in said aperture.

8. Detection device according to claim 7 characterised in that the cold shield (8) defines a closed enclosure containing the first and second photodetectors (1a, 1b) and in that the second filter (4b) is located in the closed enclosure.

9. Detection device according to claim 7 characterised in that the cold shield (8) defines a closed enclosure containing the first and second photodetectors (1a, 1b) and in that the second filter (4b) is located outside the closed enclosure.

10. Fabrication method of a multispectral detection device characterised in that it comprises the following steps: - providing a substrate comprising first and second photodetectors (1a and 1b) and a continuous passivation layer monolithically covering the first and second photodetectors (1a, 1b), the passivation layer having a thickness of between 10nm and 2000nm, the first and second photodetectors (1a, 1b) each being sensitive to a first wavelength range and to a second wavelength range different from the first wavelength range, the first photodetector (1a) delivering a first signal representative of the received radiation and the second photodetector (1b) delivering a second signal representative of the received radiation, the first and second wavelength ranges being ranges of the infrared radiation, - forming a first filter (4a) configured to allow the first wavelength range to pass and to block the second wavelength range, the first filter (4a) covering the first photodetector (1a) and leaving the second photodetector (1b) uncovered, the first filter (4a) being arranged on the passivation layer and the first photodetector (1a) so as to block the passage of the second wavelength range into the first photodetector (1a), the first filter (4a) being separated from the first photodetector (1a) by the passivation layer, the first filter (4a) generating thermomechanical stresses in the first photodetector (1a) and in the second photodetector (1b), - forming a second filter (4b) arranged at a distance from the first and second photodetectors (1a, 1b) and at a distance from the first filter (4a), the second filter (4b) being configured to allow the first wavelength range and the second wavelength range to pass, the second filter (4b) being configured to block a higher wavelength than the longest of the wavelengths in the first and second wavelength ranges and / or to block a lower wavelength than the shortest of the wavelengths in the first and second wavelength ranges, the first filter (4a) and the second filter (4b) being arranged successively in the optical path of the first photodetector (1a), the second filter (4b) being common to the first photodetector (1a) and the second photodetector (1b), the passivation layer smoothing thermomechanical stresses on the first and second photodetectors (1a, 1b).

11. Fabrication method according to claim 10 comprising, before the second filter (4b) is formed: - forming a third filter (4c) configured to allow the second wavelength range to pass and to block the first wavelength range, the third filter (4c) covering the second photodetector (1b) and leaving the first photodetector (1a) uncovered, the third filter (4c) being in contact with the second photodetector (1b) so as to block the passage of the first wavelength range in the second photodetector (1b).