Patent Publication Number: US-2023154957-A1

Title: Structure of an angular filter on a cmos sensor

Description:
The present patent application claims the priority benefit of French patent application FR2001613 which is herein incorporated by reference. 
     FIELD 
     The present disclosure generally concerns an image acquisition device. 
     BACKGROUND 
     An image acquisition device generally comprises an image sensor and an optical system. The optical system may be an angular filter, or a set of lenses, interposed between the sensitive portion of the sensor and the object to be imaged. 
     The image sensor generally comprises an array of photodetectors capable of generating a signal proportional to the received light intensity. 
     An angular filter is a device enabling to filter an incident radiation according to the incidence of this radiation and thus to block rays having an incidence greater than a desired angle, called maximum incidence angle, which enables to form a sharp image of the object to be imaged on the sensitive portion of the image sensor. 
     SUMMARY 
     There is a need to improve image acquisition devices. 
     An embodiment overcomes all or part of the disadvantages of known image acquisition devices. 
     An embodiment provides a device comprising a stack comprising, in the order, at least:
         an image sensor in MOS technology adapted to detecting a radiation;   a first array of lenses;   a structure formed of at least a first matrix of openings delimited by walls opaque to said radiation; and   a second array of lenses.       

     According to an embodiment, the number of lenses of the second array is greater than the number of lenses of the first array. 
     According to an embodiment, the number of lenses of the second array is from two to ten times greater than the number of lenses of the first array, preferably, twice greater. 
     According to an embodiment, the device comprises an adhesive layer between said structure and the first array of lenses. 
     According to an embodiment, the device comprises a refraction index matching layer between said structure and the first array of lenses. 
     According to an embodiment:
         each opening of the first matrix is associated with a single lens of the second array; and   the optical axis of each lens of the second array is aligned with the center of an opening of the first matrix.       

     According to an embodiment, the structure comprises, under the first matrix of openings, a second matrix of openings, delimited by walls opaque to said radiation. The number of openings of the first matrix is identical to the number of openings of the second matrix. The center of each opening of the first matrix is aligned with the center of an opening of the second matrix. 
     According to an embodiment, the lenses of the second array and the lenses of the first array are plano-convex. The planar surfaces of the lenses of the first array and of the second array are on the sensor side. 
     According to an embodiment, the openings are filled with a material at least partly transparent to said radiation. 
     According to an embodiment, the lenses of the first array have a diameter greater than the diameter of the lenses of the second array. 
     According to an embodiment, the structure comprises a third array of plano-convex lenses, the planar surfaces of the lenses of the second lens array and of the third lens array facing one another. The third lens array is located between the first matrix of openings and the first lens array or between the first matrix of openings and the second lens array. 
     According to an embodiment, the optical axis of each lens of the second array is aligned with the optical axis of a lens of the third array. 
     According to an embodiment, the image focal planes of the lenses of the second array coincide with the object focal planes of the lenses of the third array. 
     According to an embodiment, the number of lenses of the third array is greater than the number of lenses of the second array. 
     According to an embodiment, the lenses of the second array have a diameter greater than that of the lenses of the third array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which: 
         FIG.  1    shows in a partial simplified block diagram an example of an image acquisition system; 
         FIG.  2    shows in a partial simplified cross-section view an example of an image acquisition device; 
         FIG.  3    shows in a partial simplified cross-section view an embodiment of the image acquisition device illustrated in  FIG.  2   ; 
         FIG.  4    shows in a partial simplified cross-section view another embodiment of the image acquisition device illustrated in  FIG.  2   ; 
         FIG.  5    shows in a partial simplified cross-section view still another embodiment of the image acquisition device illustrated in  FIG.  2   ; 
         FIG.  6    shows in a partial simplified cross-section view still another embodiment of the image acquisition device illustrated in  FIG.  2   ; 
         FIG.  7    shows in a partial simplified cross-section view still another embodiment of the image acquisition device illustrated in  FIG.  2   ; and 
         FIG.  8    shows in a partial simplified cross-section view still another embodiment of the image acquisition device illustrated in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties. 
     For the sake of clarity, only the steps and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the structure of the image sensor will not be precisely detailed in the present description. 
     Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements. 
     In the following disclosure, unless otherwise specified, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “upper”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures. 
     Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%. 
     In the following description, unless specified otherwise, a layer or a film is called opaque to a radiation when the transmittance of the radiation through the layer of the film is smaller than 10%. In the rest of the disclosure, a layer or a film is called transparent to a radiation when the transmittance of the radiation through the layer or the film is greater than 10%, preferably greater than 50%. According to an embodiment, for a same optical system, all the elements of the optical system which are opaque to a radiation have a transmittance which is smaller than half, preferably smaller than one fifth, more preferably smaller than one tenth, of the lowest transmittance of the elements of the optical system transparent to said radiation. In the rest of the disclosure, the expression “useful radiation” designates the electromagnetic radiation crossing the optical system in operation. 
     In the following description, the expression “micrometer-range optical element” designates an optical element formed on a surface of a support having its maximum dimension, measured parallel to said surface, greater than 1 μm and smaller than 1 mm. 
     Embodiments of optical systems will not be described for optical systems comprising an array of micrometer-range optical elements in the case where each micrometer-range optical element corresponds to a micrometer-range lens, or microlens, formed of two diopters. It should however be clear that these embodiments may also be implemented with other types of micrometer-range optical elements, where each micrometer-range optical element may for example correspond to a micrometer-range Fresnel lens, to a micrometer-range index gradient lens, or to a micrometer-range diffraction grating. 
     In the following description, “visible light” designates an electromagnetic radiation having a wavelength in the range from 400 nm to 700 nm and “infrared radiation” designates an electromagnetic radiation having a wavelength in the range from 700 nm to 1 mm. In infrared radiation, one can particularly distinguish near infrared radiation having a wavelength in the range from 700 nm to 1.7 μm. 
     In the following description, the refraction index of a material corresponds to the refraction index of the material for the wavelength range of the radiation captured by the image sensor. Unless specified otherwise, the refraction index is considered as substantially constant over the wavelength range of the useful radiation, for example, equal to the average of the refraction index over the wavelength range of the radiation captured by the image sensor. 
       FIG.  1    shows in a partial simplified block diagram an example of an image acquisition system. 
     The image acquisition system, illustrated in  FIG.  1   , comprises: 
     a. an image acquisition device  1  (DEVICE); and 
     b. a processing unit  13  (PU). 
     Processing unit  13  preferably comprises means for processing the signals delivered by device  1 , not shown in  FIG.  1   . Processing unit  13  for example comprises a microprocessor. 
     Device  1  and processing unit  13  are preferably coupled by a link  15 . Device  1  and the processing unit are for example integrated in a same circuit. 
       FIG.  2    shows in a partial simplified cross-section view an example of an image acquisition device  1 . 
     More particularly,  FIG.  2    shows image acquisition device  1  and a source  25  emitting a radiation  27 . 
     Image acquisition device  1 , illustrated in  FIG.  2   , comprises from bottom to top:
         an image sensor  17  (SENSOR) in complementary metal oxide semiconductor (CMOS) technology, which may be coupled to photodetectors or inorganic (polysilicon) or organic photodiodes adapted to detecting radiation  27 ;   a first array of lenses  19  (LENS 1 );   an array structure  21  (LAYER(S));   a second array of lenses  23  (LENS 2 ); and   an object  24 .       

     Structure  21  and second lens array  23  preferably form an optical filter  2  or angular filter. Image sensor  17  and first lens array  19  preferably form a CMOS imager  3 . 
     Radiation  27  is for example in the visible range and/or in the infrared range. It may be a radiation of a single wavelength or a radiation of a plurality of wavelengths (or wavelength range). 
     Light source  25  is illustrated, in  FIG.  2   , above object  24 . It may however as a variant be located between object  24  and filter  2 . 
     In the case of an application to the determination of fingerprints, object  24  corresponds to a user&#39;s finger. 
       FIG.  3    shows in a partial simplified cross-section view an embodiment of the image acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  3    shows an image acquisition device  101  in which array structure  21  is formed of a layer  211  comprising a first matrix of openings  41  delimiting walls  39  opaque to said radiation. 
     Image acquisition device  101 , illustrated in  FIG.  3   , comprises from bottom to top:
         CMOS imager  3 , formed of:
           image sensor  17  (not detailed in the drawings) preferably formed of a substrate, of readout circuits, of conductive tracks, and of photodiodes,   a first passivation (insulating) layer  29  on top of and in contact with image sensor  17 ,   a second layer  31  playing the role of a color filter covering first layer  29  full plate, and   first plano-convex lens array  19 , having its planar surfaces on the side of sensor  17 , covered with a third passivation layer  33 ;   
           a fourth optical index matching layer  35  covering layer  33 ;   a fifth layer  37  or adhesive on top of and in contact with layer  35 ; and   angular filter  2  formed of:
           structure  21  comprising layer  211  of openings  41  and having its walls  39  on top of and in contact with fifth layer  37 ,   a substrate  43  covering structure  21 , and   second plano-convex lens array  23 , having its planar surfaces on the sensor side, covered with a sixth layer  45 .   
               

     First lens array  19  for example enables to focus the rays incident to lenses  19  onto the photodetectors present in image sensor  17 . 
     According to an embodiment, the lens array  19  within imager  3  forms a pixel array where a pixel corresponds, for example, substantially to the square having the circle corresponding to the surface of a lens  19  inscribed therein. Each pixel thus comprises a lens  19  substantially centered on the pixel. For example, all lenses  19  have substantially the same diameter. The diameter of lenses  19  is preferably substantially identical to the length of the pixel sides. 
     According to an embodiment, the pixels of CMOS imager  3  are substantially square. The length of the pixel sides is preferably in the range from 0.7 μm to 50 μm and is more preferably in the order of 30 μm. 
     According to an embodiment, imager  3  is substantially square. The length of the sides of imager  3  is preferably in the range from 5 mm to 50 mm, and is more preferably in the order of 10 mm. 
     Layer  31  is preferably made of a material absorbing wavelengths in the range from approximately 400 nm to 600 nm (cyan), preferably from 470 nm to 600 nm (green). 
     Layer  29  may be made of an inorganic material, for example, of silicon oxide (SiO 2 ), of silicon nitride (SiN), or of a combination of these two materials (for example, a multilayer stack). 
     Insulating layer  29  may be made of a fluorinated polymer, particularly Bellex&#39;s fluorinated polymer known under trade name “Cytop”, of polyvinylpyrrolidone (PVP), of polymethyl methacrylate (PMMA), of polystyrene (PS), of parylene, of polyimide (PI), of acrylonitrile butadiene styrene (ABS), of poly(ethylene terephthalate) (PET), of poly(ethylene naphthalate) (PEN), of cyclo olefin polymer (COP), of polydimethylsiloxane (PDMS), of a photolithography resin, of epoxy resin, of acrylate resin, or of a mixture of at least two of these compounds. 
     As a variant, layer  29  may be made of an inorganic dielectric, particularly of silicon nitride, of silicon oxide, or of aluminum oxide (Al 2 O 3 ). 
     Layer  33  is preferably a passivation layer which takes the shape of microlenses  19  and which enables to insulate and planarize the surface of imager  3 . Layer  33  may be made of an inorganic material, for example, of silicon oxide (SiO 2 ) or of silicon nitride (SiN), or of a combination of these two materials (for example, a multilayer stack). 
     According to the embodiment illustrated in  FIG.  3   , optical filter  2 , by the association of the second array of lenses  23  and of layer  211 , is adapted to filtering the incident radiation according to its angle of incidence relative to the optical axes of the lenses  23  of the second array. 
     According to the embodiment illustrated in  FIG.  3   , angular filter  2  is adapted so that the photodetectors of image sensor  17  only receive rays having respective incidences, relative to the optical axes of lenses  23 , smaller than a maximum angle of incidence smaller than 45°, preferably smaller than 20°, more preferably smaller than 5°, more preferably still smaller than 3°. Angular filter  2  is capable blocking the rays of the incident radiation having respective incidences relative to the optical axes of the lenses  23  of filter  2  greater than the maximum incidence angle. 
     According to the embodiment illustrated in  FIG.  3   , each opening  41  of layer  211  is associated with a single lens  23  of the second array and each lense  23  is associated with a single opening  41 . Lenses  23  preferably meet. The optical axes of lenses  23  are preferably aligned with the centers of openings  41 . The diameter of the lenses  23  of the second array is preferably greater than the maximum cross-section (measured perpendicularly to the optical axis of lenses  23 ) of openings  41 . 
     Walls  39  are for example opaque to radiation  27 , for example, absorbing and/or reflective for radiation  27 . Walls  39  are preferably opaque for wavelengths in the range from 400 nm to 600 nm (cyan and green), used for imaging (biometry and fingerprint imaging). Call “h” the height of walls  39  (measured in a plane parallel to the optical axes of lenses  23 ). 
     According to an embodiment, openings  41  are arranged in rows and in columns. Openings  41  may have substantially the same dimensions. Call “w 1 ” the diameter of openings  41  (measured at the base of the openings, that is, at the interface with substrate  43 ). The diameter of each lens  23  is preferably greater than the diameter w 1  of the opening  41  having lens  23  associated therewith. 
     According to an embodiment, openings  41  are regularly arranged in rows and in columns. Call “p” the repetition pitch of openings  41 , that is, the distance in top view between centers of two successive openings  41  of a row or of a column. 
     In  FIG.  3   , openings  41  are shown with a trapezoidal cross-section. Generally, openings  41  may be square, triangular, rectangular, funnel-shaped. In the shown example, the width (or diameter) of openings  41 , at the level of the upper surface of layer  211 , is greater than the width (or diameter) of openings  41 , at the level of the lower surface of layer  211 . 
     Openings  41 , in top view, may be circular, oval, or polygonal, for example, triangular, square, rectangular, or trapezoidal. Openings  41 , in top view, are preferably circular. 
     The resolution of optical filter  2 , in cross-section (plane XZ or YZ), is preferably greater than the resolution of image sensor  17 , preferably from two to ten times greater. In other words, there are, in cross-section (plane XZ or YZ), from two to ten times more openings  41  than lenses  19  of the first array. Thus a lens  19  is associated with at least four openings  41  (two openings in plane YZ and two openings in plane XZ). 
     An advantage is that the difference between the resolution of imager and that of angular filter  2  enables to decrease the constraints of alignment of filter  2  on imager  3 . 
     For example, lenses  23  have substantially the same diameter. The diameter of the lenses  19  of the first array is thus greater than the diameter of the lenses  23  of the second array. 
     Width w 1  is, in practice and preferably, smaller than the diameter of lenses  23  so that layer  39  has a sufficient bonding to substrate  43 . Width w 1  is preferably in the range from 0.5 μm to 25 μm, for example equal to approximately 10 μm. Pitch p may be in the range from 1 μm to 25 μm, preferably in the range from 12 μm to 20 μm. Height h is, for example, in the range from 1 μm to  1  mm, preferably in the range from 12 μm to 15 μm. 
     According to this embodiment, microlenses  23  and substrate  43  are preferably made of materials which are transparent or partially transparent, that is, transparent in a portion of the considered spectrum for the targeted field, for example, imaging, over the wavelength range corresponding to the wavelengths used during the exposure. 
     Substrate  43  may be made of a transparent polymer which does not absorb at least the considered wavelengths, here in the visible and infrared range. The polymer may in particular be made of polyethylene terephthalate PET, poly(methyl methacrylate) PMMA, cyclic olefin polymer (COP), a polyimide (PI), or of polycarbonate (PC). Substrate  43  is preferably made of PET. The thickness of substrate  43  may for example vary from 1 to 100 μm, preferably from 10 to 50 μm. Substrate  43  may correspond to a colored filter, to a polarizer, to a half-wave plate or to a quarter-wave plate. 
     According to an embodiment, microlenses  23  and  19  are made of materials having a refraction index in the range from 1.4 to 1.7 and preferably in the order of 1.6. Microlenses  23  and  19  may be made of silica, of PMMA, of a positive resist, of PET, of polyethylene naphthalate (PEN), of COP, of polydimethylsiloxane (PDMS)/silicone, of epoxy resin, or of acrylate resin. Microlenses  23  and  19  may be formed by flowing of resist blocks. Microlenses  19  and  23  may further be formed by molding on a layer of PET, PEN, COP, PDMS/silicone, of epoxy resin, or of acrylate resin. Microlenses  19  and  23  may finally be formed by nano-imprint. 
     As a variant, each microlens is replaced with another type of micrometer-range optical element, particularly a micrometer-range Fresnel lens, a micrometer-range index gradient lens, or micrometer-range diffraction grating. The microlenses are converging lenses, each having a focal distance f in the range from 1 μm to 100 μm, preferably from 1 μm to 50 μm. According to an embodiment, all microlenses  19  are substantially identical and all microlenses  23  are substantially identical. 
     According to an embodiment, layer  45  is a filling layer which follows the shape of microlenses  23 . Layer  45  may be obtained from an optically clear adhesive (OCA), particularly a liquid optically clear adhesive (LOCA), or a material with a low refraction index, or an epoxy/acrylate glue, or a film of a gas or of a gaseous mixture, for example, air. 
     Preferably, layer  45  is made of a material having a low refraction index, smaller than that of the material of microlenses  23 . For example, the difference between the refraction index of the material of lenses  23  and the refraction index of the material of layer  45  is preferably in the range from 0.5 to 0.1. The difference between the refraction index of the material of lenses  23  and the refraction index of the material of layer  45  is more preferably in the order of 0.15. Layer  45  may be made of a filling material which is a non-adhesive transparent material. 
     According to another embodiment, layer  45  corresponds to a film which is applied against microlens array  23 , for example an OCA film. In this case, the contact area between layer  45  and microlenses  23  may be decreased, for example, limited to the tops of microlenses  23 . 
     According to an embodiment, openings  41  are filled with air or with a filling material at least partially transparent to the radiation detected by the photodetectors, for example, PDMS, an epoxy or acrylate resin, or a resin known under trade name SU 8 . As a variant, openings  41  may be filled with a partially absorbing material, that is, a material absorbing in a portion of the considered spectrum for the targeted field, for example, imaging, to chromatically filter the rays angularly filtered by filter  2 . As a variant, the filling material of openings  41  is opaque to radiation in near infrared. In the case where openings  41  are filled with a material, said material may for example form a layer between walls  39  and the underlying layer  37  so that walls  39  are not in contact with layer  37 . 
     Angular filter  2  preferably has a thickness in the order of 50 μm. 
     Angular filter  2  and imager  3  are for example assembled by an adhesive layer  37 . Layer  37  is for example made of a material selected from an acrylate glue, an epoxy glue, or an OCA. Layer  37  is preferably made of an acrylate glue. 
     Layer  35  is a refraction index matching layer, that is, it enables to decrease losses of light rays by reflection at the interface between the angular filter (the filling material of openings  41 ) and passivation layer  33 . Layer  35  is preferably made of a material having a refraction index between the refraction index of layer  33  and the refraction index of the filling material of openings  41 . 
     According to an implementation mode, layer  35  is deposited on the front surface of imager  3  (the upper surface in the orientation of  FIG.  3   ) by printing, by transfer of a film (lamination), or by evaporation, at the end of the manufacturing of imager  3 . 
     According to an implementation mode, layer  37  is deposited on the rear surface of angular filter  2  (the lower surface in the orientation of  FIG.  3   ) by printing or by transfer of a film (lamination). 
     As variant, layer  37  is deposited on the front surface of layer  35  of imager  3 . 
     The assembly of filter  2  and of imager  3  is for example performed after the deposition of layer  37  by lamination of filter  2  at the surface of imager  3  (more particularly on the surface of layer  35 ). 
     According to an implementation mode, a step of anneal, of ultraviolet crosslinking, or of autoclave pressurization, follows the assembly to optimize the mechanical bonding properties. 
     According to an embodiment, not shown in  FIG.  3   , device  101  comprises an additional layer, for example, between filter  2  and imager  3 . This layer corresponds to an infrared filter enabling to filter radiations having a wavelength greater than 600 nm. The transmittance of this infrared filter is preferably smaller than 0.1% (OD3 (Optical Density of 3)). 
     According to the considered materials, the method of forming at least certain layers may correspond to a so-called additive process, for example, by direct printing of the material forming the layers at the desired locations, particularly in sol-gel form, for example, by inkjet printing, photogravure, silk-screening, flexography, spray coating, or drop casting. 
     According to the considered materials, the method of forming at least certain layers may correspond to a so-called subtractive method, where the material forming the layers is deposited over the entire structure and where the non-used portions are then removed, for example, by photolithography or laser ablation. 
     According to the considered material, the deposition over the entire structure may be performed, for example, by liquid deposition, by cathode sputtering, or by evaporation. Methods such as spin coating, spray coating, heliography, slot-die coating, blade coating, flexography, or silk-screening, may in particular be used. When the layers are metallic, the metal is for example deposited by evaporation or by cathode sputtering over the entire support and the metal layers are delimited by etching. 
     Advantageously, at least some of the layers may be formed by printing techniques. The materials of the previously-described layers may be deposited in liquid form, for example, in the form of conductive and semiconductor inks by means of inkjet printers. “Materials in liquid form” here also designates gel materials capable of being deposited by printing techniques. Anneal steps may be provided between the depositions of the different layers, but it is possible for the anneal temperatures not to exceed 150° C., and the deposition and the possible anneals may be carried out at the atmospheric pressure. 
       FIG.  4    shows in a partial simplified cross-section view another embodiment of the image acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  4    shows an image acquisition device  102  similar to the image acquisition device  101  illustrated in  FIG.  3   , with the difference that the array of second lenses comprises lenses  23 ′ smaller than lenses  23  ( FIG.  3   ). 
     The number of lenses  23 ′ in device  102  is preferably greater than the number of openings  41  (in plane XY). As an example, the number of lenses  23 ′ is four times greater than the number of openings  41 . Lenses  23 ′ have, according to the embodiment illustrated in  FIG.  4   , a diameter smaller than the diameter w 1  of openings  41 . 
     An advantage of the embodiment illustrated in  FIG.  4    is that it requires no alignment of the second array of lenses  23 ′ on the matrix of openings  41 . 
       FIG.  5    shows in a partial simplified cross-section view still another embodiment of the example of the image acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  5    shows an image acquisition device  103  similar to the image acquisition device  101  illustrated in  FIG.  3   , with the difference that array structure  21  comprises a third lens array  47 . 
     The third array of plano-convex lenses  47  is used for the collimation of the light transmitted by the matrix of openings  41  coupled to the second lens array  23 . The planar surfaces of lenses  47  face the planar surfaces of lenses  23 . The third array is located between layer  211  and imager  3 . 
     In the embodiment shown in  FIG.  5   , the number of lenses  47  of the third array is equal to the number of lenses  23  of the second array. The lenses  47  of the third array and the lenses  23  of the second array are aligned by their optical axes. 
     As a variant, the number of lenses  47  of the third array is more significant than the number of levels  23  of the second array. 
     Lenses  47  meet or not. 
     The rays emerge from lenses  23  and from layer  211  with an angle α relative to the respective direction of the rays incident to lenses  23 . Angle α is specific to a lens  23  and depends on the diameter thereof and on the focal distance of this same lens  23 . 
     As they come out of layer  211 , the rays meet the lenses  47  of the third array. The rays are thus deviated, as they come out of lenses  47 , by an angle β relative to the respective directions of the rays incident to lenses  47 . Angle β is specific to a lens  47  and depends on the diameter thereof and on the focal distance of this lens  47 . 
     A total divergence angle corresponds to the deviations successively generated by lenses  23  and by lenses  47 . The lenses  47  of the third array are selected so that the total divergence angle is for example smaller than or equal to approximately 5°. 
     The embodiment shown in  FIG.  5    illustrates an ideal configuration where the image focal planes of the lenses  23  of the second array are the same as the object focal planes of the lenses  47  of the third array. The shown rays, arriving parallel to the optical axis, are focused on the image focus of lens  23  or object focus of lens  47 . The rays which emerge from lens  47  thus propagate parallel to the optical axis thereof. The total divergence angle is, in this case, zero. 
     Third lens array  47  is, in  FIG.  5   , located under and in contact with a seventh layer  40 . Seventh layer  40 , originating from the filling of openings  41 , covers the rear surfaces of walls  39 . 
     As a variant, the third array of lenses  47  is located on top of and in contact with the rear surface of walls  39 . Openings  41  are then filled with air or with a filling material. 
     Lenses  47  and lenses  23  have the same composition or different compositions. 
     According to the embodiment of  FIG.  5   , the rear surface of lenses  47  is covered with an eighth filling layer  49 . Layer  49  and layer  45  may have the same composition or different compositions. Layer  49  preferably has a refraction index smaller than the refraction index of the material of lenses  47 . 
     In the absence of a third lens array  47 , if the divergence angle is too large, the rays emerging from a lens  23  would risk illuminating a plurality of photodetectors or pixels. This generates a loss of resolution in the quality of the resulting image. 
     An advantage that appears is that the presence of a third array of lenses  47  generates a decrease in the divergence angle at the output of angular filter  2 . The decrease of the divergence angle enables to decrease risks of intersection of the rays emerging at the level of imager  3 . 
       FIG.  6    shows in a partial simplified cross-section view still another embodiment of the example of the image acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  6    shows an image acquisition device  104  similar to the image acquisition device  103  illustrated in  FIG.  5   , with the difference that it comprises lenses  47 ′ smaller than lenses  47  ( FIG.  5   ). 
     The number of lenses  47 ′ in device  104  is preferably greater than the number of openings  41 . As an example, the number of lenses  47 ′ is four times greater than the number of openings  41  (in plane XY). 
     An advantage of the embodiment illustrated in  FIG.  6    is that it requires no alignment of third lens array  47 ′ on the matrix of openings  41 . 
       FIG.  7    shows in a partial simplified cross-section view still another embodiment of the example of the acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  7    shows an image acquisition device  105  similar to the image acquisition device  103  illustrated in  FIG.  5   , with the difference that third lens array  47 ″ is located between second lens array  23  and layer  211  of openings  41 . 
     In the shown example, device  105  comprises a filling layer  51  covering the rear surface of lenses  47 . Layer  51  is similar to the layer  49  of the device  103  illustrated in  FIG.  5   , with the difference that it rests on the upper surface of layer  211 . 
       FIG.  8    shows in a partial simplified cross-section view still another embodiment of the example of the acquisition device illustrated in  FIG.  2   . 
     More particularly,  FIG.  8    shows an image acquisition device  106  similar to the image acquisition device  101  illustrated in  FIG.  3   , with the difference that array structure  21  comprises a ninth layer  213  formed of a second matrix of openings  53  delimiting walls  55  opaque to radiation  27  ( FIG.  2   ). 
     According to the embodiment illustrated in  FIG.  8   , layer  213  is located under and in contact with the seventh layer  40  resulting from the filling of openings  41  with the filling material. Seventh layer  40  covers the rear surfaces of walls  39 . 
     AS a variant, layer  213  is located on top of and in contact with the rear surface of walls  39 . Openings  41  are then filled with air or with a filling material. 
     Openings  53  for example have substantially the same shape as openings  41 , with the difference that the dimensions of openings  41  and  53  may be different. Walls  55  for example have substantially the same shape and the same composition as walls  39 , with the difference that the dimensions of walls  39  and  55  may be different. 
     According to the embodiment illustrated in  FIG.  8   , layer  213  comprises a number of openings  53  substantially identical to the number of openings  41  present in the matrix of layer  211 . Preferably, the number of openings  41  is identical to the number of openings  53 . Each opening  41  is preferably aligned with an opening  53 , for example, the center of each opening  41  is aligned with the center of an opening  53 . 
     According to an embodiment, openings  53  and openings  41  have the same dimensions, that is, openings  53  have a diameter “w 2 ” (measured at the base of the openings, that is, at the interface with layer  40 ) substantially identical to the diameter w 1  of openings  41 . Preferably, diameters w 1  and w 2  are identical. Walls  55  for example have a height h 2  substantially identical to the height h of walls  39 . Preferably, heights h and h 2  are identical. 
     As a variant, diameters w 1  and w 2  are different. In this case, diameter w 2  is, preferably, smaller than diameter w 1 . 
     According to another variant, heights h and h 2  are different. 
     According to an embodiment, openings  53  are filled with air or, preferably, with a filling material having a composition similar to that of the filling material of openings  41 . More preferably still, the filling material fills openings  53  and forms a layer  57  on the rear surface of walls  55 . 
     Various embodiments and variants have been described. 
     Those skilled in the art will understand that certain features of these various embodiments and variants may be combined, and other variants will occur to those skilled in the art. In particular, the embodiments illustrated in  FIGS.  4  to  8    may be combined. Further, the described embodiments and implementation modes are for example not limited to the examples of dimensions and of materials mentioned hereabove. 
     Finally, the practical implementation of the described embodiments and variations is within the abilities of those skilled in the art based on the functional indications given hereabove.