FR3135794A1 - Optical filter for photodetectors - Google Patents

Abstract

Optical filter for photodetectors The present description relates to an optical filter intended to cover a matrix of photodetectors, the optical filter comprising a plurality of identical elementary filter patterns (41) regularly distributed over the surface of the optical filter, each filter pattern (41) comprising a arrangement of at least two color filters (43, 43v, 43ir, 43r, 43b, 43g) joined together, two neighboring elementary filter patterns (41) being spaced apart by the size of at least two photodetectors. Figure for abstract: Fig. 2

Description

Optical filter for photodetectors

The present description generally relates to an optical filter intended to cover photodetectors within an image acquisition device and, more particularly, a fingerprint acquisition device.

Fingerprint acquisition devices are used in many areas, for example, to secure devices, secure buildings, control access or control the identities of individuals.

As data, information and access protected by fingerprint sensors multiply, fingerprint acquisition devices are the target of numerous frauds.

The most common frauds are photocopies of fingers or fingerprints or the reconstruction of fingers or fingerprints in resin, silicone, latex or gelatin.

There is a need to improve and secure fingerprint acquisition devices.

One embodiment provides an optical filter intended to cover a matrix of photodetectors, the optical filter comprising a plurality of identical elementary filter patterns regularly distributed over the surface of the optical filter, each filter pattern comprising an arrangement of at least two adjacent color filters , two neighboring elementary filter patterns being spaced by the size of at least two photodetectors.

According to one embodiment, each color filter has an area corresponding to the area of at least one sub-matrix of two by two adjacent photodetectors.

According to one embodiment, two filter patterns are spaced by the size of at least four photodetectors in the direction of the rows of the matrix and by the size of at least four photodetectors in the direction of the columns of the matrix.

According to one embodiment, the filter patterns are positioned within the optical filter so that zones extending over the entire length or the entire width of the optical filter are not covered by the filter patterns, the zones having a width equal to the width of at least two photodetectors.

According to one embodiment, the filter patterns comprise at least three adjacent color filters, at least one of the at least three color filters corresponding to a superposition of the other color filters.

According to one embodiment, each of the other color filters allows a wavelength band of visible radiation and infrared radiation to pass.

According to one embodiment, said at least one of the at least three color filters allows only infrared radiation to pass.

According to one embodiment, each filter pattern comprises three color filters arranged in an “L” shape.

According to one embodiment, each filter pattern comprises four color filters arranged in a square.

According to one embodiment, each filter pattern comprises four color filters arranged in a "T".

Another embodiment provides an image acquisition device comprising a photodetector sensor and an optical filter as defined above.

According to one embodiment, the photodetectors are organic.

According to one embodiment, the device comprises an angular filter, different from the optical filter.

According to one embodiment, the device comprises a processing unit.

These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given on a non-limiting basis in relation to the attached figures, among which:

there illustrates, through a partial and schematic sectional view, an embodiment of an image acquisition device;

there represents, in a partial and schematic top view, an embodiment of the image acquisition device of the ;

there represents, in a partial and schematic top view, another embodiment of the image acquisition device of the ;

there represents, in a partial and schematic top view, yet another embodiment of the image acquisition device of the ; And

there represents, through a partial and schematic perspective view, an embodiment of the image acquisition device of the .

The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the operation of an image sensor and the exploitation of the data by a processing unit have not been detailed, the present description being compatible with usual image sensors or these elements being within the reach of the skilled person from the information in this description.

Unless otherwise specified, when we refer to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when we refer to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be linked through one or more other elements.

In the following description, when referring to absolute position qualifiers, such as "front", "back", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "superior", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc., it is referred to unless otherwise specified in the orientation of the figures.

Unless otherwise specified, the expressions "approximately", "approximately", "substantially", and "of the order of" mean to the nearest 10%, preferably to the nearest 5%.

In the remainder of the description, unless otherwise specified, a layer or film is said to be opaque to radiation when the transmittance of the radiation through the layer or film is less than 10%. In the remainder of the description, a layer or film is said to be transparent to radiation when the transmittance of the radiation through the layer or film is greater than 10%. According to one embodiment, for the same optical system, all the elements of the optical system which are opaque to radiation have a transmittance which is less than half, preferably less than a fifth, more preferably less than a tenth, of the transmittance. weaker elements of the optical system transparent to said radiation. In the remainder of the description, “useful radiation” refers to the electromagnetic radiation passing through the optical system in operation.

In the remainder of the description, an optical element formed on one face of a support whose maximum dimension, measured parallel to said face, is greater than 1 µm and less than 1 mm, is called "micrometric-sized optical element". We call the wavelength of radiation, or the central or main wavelength of the radiation, the wavelength at which the maximum of the spectrum of the radiation is reached.

Embodiments of optical systems will now be described for optical systems comprising a matrix of micrometric-sized optical elements in the case where each micrometric-sized optical element corresponds to a micrometric-sized lens, or microlens, composed of two diopters. . However, it is clear that these embodiments can also be implemented with other types of micrometric-sized optical elements, each micrometric-sized optical element being able to correspond, for example, to a micrometric-sized Fresnel lens, to a micrometer-sized gradient index lens or to a micrometer-sized diffraction grating.

In the remainder of the description, visible light is electromagnetic radiation whose wavelength is between 400 nm and 700 nm, and, in this range, red light is electromagnetic radiation whose wavelength is between 600 nm. nm and 700 nm, blue light is electromagnetic radiation whose wavelength is between 430 nm and 490 nm and green light is electromagnetic radiation whose wavelength is between 510 nm and 570 nm. Infrared radiation is electromagnetic radiation whose wavelength is between 700 nm and 1 mm. Infrared radiation, we distinguish in particular near infrared radiation whose wavelength is between 700 nm and 1.1 µm.

Unless otherwise specified, the expressions "all elements", "all elements", "each element", mean between 95% and 100% of the elements.

The inventors have demonstrated that it is possible to distinguish a real finger from a false finger from images acquired at different wavelengths. More precisely, the inventors have noted that it is possible to distinguish a real finger from a false finger from at least one image acquired in an infrared wavelength and an image acquired in a length of wave of the visible.

It is therefore interesting, for biometric uses, to overcome the image sensors with filters comprising parts filtering in the visible and parts filtering in the infrared.

The presence of these color filters can, however, disrupt the operation of the image processing implemented to reconstruct a fingerprint and identify a user from this fingerprint. For example, the processing operations implemented may include weighting or normalization of the response of each photodetector of a matrix sensor by a value representative of the average of the responses of all the photodetectors of the same line. However, the presence of color filters can distort this average value, the light intensity perceived by the photodetectors covered by a color filter being different from that perceived by the photodetectors not covered by a color filter.

There illustrates, in a partial and schematic sectional view, an embodiment of an image acquisition device 1.

The image acquisition device 1 comprises an image sensor 11 comprising photodetectors 21, for example photodiodes. The device 1 is adapted to capture the image response of an object 17, partially represented, preferably a finger located opposite the upper face of the device 1 and thus of the image sensor 11. For this, the sensor 11 is adapted to detect radiation 15, emitted in part by a light source (not shown) which is reflected on the object 17. The light source is, for example located between the sensor 11 and the object 17, by example between the upper face of device 1 and object 17.

The light source consists, for example, of one or more light-emitting diodes (LED, Light-Emitting Diode), possibly associated with a waveguide layer. Alternatively, the light source consists of one or more organic light-emitting diodes (OLEDs, Organic Light-Emitting Diode), also optionally associated with a waveguide layer. If the light source includes several diodes, they may be identical and emit the same radiation. Alternatively, the sources can be different and emit different radiations, all of the different radiations partly forming the radiation 15. The radiation emitted by the light source is, for example, called useful radiation.

By way of example, in addition to the useful radiation emitted by the light source, the radiation 15 comprises so-called parasitic radiation coming from the environment external to the device 1. The parasitic radiation includes, for example, wavelengths in the visible and/or in the infrared.

The radiation 15 then comprises, for example, at least part of the visible wavelengths and, for example, part of the infrared wavelengths.

In the present description, the embodiments of the devices of Figures 1 to 5 are represented in space according to a direct orthogonal XYZ reference, the Y axis of the XYZ reference being orthogonal to the upper face of the sensor 11.

By way of example, the device 1 comprises a processing unit 19 comprising, for example, a microprocessor (not shown). The processing unit 19 may correspond to a computer or a portable telephone (smartphone).

For example, the photodetectors 21 of the image sensor 11 are organic photodiodes (OPD, Organic Photodiode) integrated on a CMOS transistor substrate (Complementary Metal Oxide Semiconductor) or a TFT transistor substrate (Thin Film Transistor).

Alternatively, the photodetectors 21 are non-organic photodiodes, for example, made from amorphous silicon or crystalline silicon. For example, photodiodes 21 are composed of quantum dots.

The photodetectors 21 are, for example, arranged in matrix form. Each photodetector 21 is preferably of substantially square shape in the XZ plane. Alternatively, the photodetectors 21 are round, rectangular of another random shape.

The photodetectors 21 have, for example, all the same structure and the same properties/characteristics. In other words, all the photodetectors 21 are, for example, substantially identical except for manufacturing differences.

By way of example, the device 1 comprises a first optical filter 18 on and in contact with the upper face of the image sensor 11, in the orientation of the . The optical filter 18 is, for example an angular filter.

1. une première couche 23 comprenant des ouvertures 25, ou trous, et des murs 27 opaques au rayonnement 15. Les ouvertures 25 sont, par exemple, comblées par un matériau formant, sur la face inférieure de la couche 23, une couche 29 ;
2. un substrat ou support 31, reposant sur la face supérieure de la couche 23 ; et
3. un réseau de lentilles 33 de taille micrométrique, situé sur la face supérieure du substrat 31, la face plane des lentilles 33 et la face supérieure du substrat 31 se faisant face. Le réseau de lentilles 33 est surmonté par une couche 35 d'aplanissement.

The optical filter 18 comprises from bottom to top in the orientation of the :

1. a first layer 23 comprising openings 25, or holes, and walls 27 opaque to radiation 15. The openings 25 are, for example, filled with a material forming, on the lower face of layer 23, a layer 29;
2. a substrate or support 31, resting on the upper face of layer 23; And
3. an array of lenses 33 of micrometric size, located on the upper face of the substrate 31, the flat face of the lenses 33 and the upper face of the substrate 31 facing each other. The lens array 33 is surmounted by a flattening layer 35.

The substrate 31 can be made of a transparent polymer which does not absorb, at least, the wavelengths considered, here in the visible range and, for example, the infrared. This polymer may in particular be poly(ethylene terephthalate) PET, poly(methyl methacrylate) PMMA, cyclic olefin polymer (COP), polyimide (PI), or polycarbonate (PC). The thickness of the substrate 31 can, for example, vary between 1 µm and 100 µm, for example between 10 µm and 100 µm. Substrate 31 may correspond to a colored filter, a polarizer, a half-wave plate or a quarter-wave plate.

The lenses 33 can be made of silica, of PMMA, of a positive photosensitive resin, of PET, of poly(ethylene naphthalate) (PEN), of COP, of polydimethylsiloxane (PDMS)/silicone, of epoxy resin or of resin acrylate. The lenses 33 can be formed by flow of blocks of a photosensitive resin. The lenses 33 can, in addition, be formed by molding on a layer of PET, PEN, COP, PDMS/silicone, epoxy resin or acrylate resin. The lenses 33 are converging lenses each having a focal length f of between 1 µm and 100 µm, for example between 1 µm and 70 µm. According to one embodiment, all the lenses 33 are substantially identical except for manufacturing differences. The lenses have, for example, a diameter of between 10 µm and 100 µm, for example equal to approximately 20 µm .

The lenses 33 and the substrate 31 are preferably made of transparent or partially transparent materials, that is to say transparent in part of the spectrum considered for the targeted field, for example imaging, over the length range waves corresponding to the wavelengths used during exposure, for example the visible ranges and, for example, the infrared.

According to one embodiment, layer 35 is a layer which matches the shape of lenses 33. Layer 35 may correspond to an optically transparent adhesive (Optically Clear Adhesive - OCA), in particular a liquid optically transparent adhesive (Liquid Optically Clear Adhesive - LOCA), or to a material with a low refractive index, (for example an epoxy/acrylate glue) or to a film of a gas or a gas mixture, for example air.

The openings 25 are, for example, filled with air, partial vacuum or a material that is at least partially transparent in the visible and infrared domains.

The angular filter 18 is adapted to filter the incident radiation as a function of the incidence of the radiation relative to the optical axes of the lenses 33.

The angular filter 18 is, more particularly, adapted so that each photodetector 21 of the image sensor 11 receives only the rays whose respective incidences with respect to the respective optical axes of the lenses 33 associated with this photodetector 21 are less than a maximum incidence less than 45°, for example less than 30°, for example less than 10°, for example less than 5°. The angular filter 18 is adapted to block the rays of the incident radiation whose respective incidences with respect to the optical axes of the lenses 33 of the optical filter 18 are greater than the maximum incidence.

Each opening 25 is preferably associated with a single lens 33. The optical axes of the lenses 33 are, for example, centered with the centers of the openings 25 of the layer 23. The diameter of the lenses 33 is, for example, greater than the maximum size of the section (perpendicular to the optical axis of the lenses 33) of the openings 25.

Each photodetector 21 is, for example, associated with at least four openings 25 (and four lenses 33). For example, each photodetector 21 is associated with exactly four openings 25. As a variant, the organization of the array of lenses 33 and openings 25 is hexagonal. In this case, each photodetector 21 is for example associated with at least five openings 25.

The device 1 is preferably divided into pixels 37. The term pixel is used to define a part of the image sensor 11 comprising a single photodetector 21. The name pixel can be applied to the scale of the image sensor 11 but also on the scale of the device 1. On the scale of the device 1, a pixel corresponds to the entire stack, constituting said device 1, directly above the pixel of the sensor 11. Overall of this description, the term pixel, unless otherwise specified, refers to a pixel on the scale of the device 1.

In the example of the , a pixel 37 corresponds to each part of the device 1 comprising, among other things, a photodetector 21, for example surmounted by four openings 25, themselves for example surmounted by four lenses 33. Each pixel 37 is, preferably, of substantially square shape seen in the XZ plane. For example, the area of each pixel is for example between 10 µm per 10 µm and 150 µm per 150 µm, for example between 50 µm per 50 µm and 90 µm per 90 µm, for example equal to approximately 50.8 µm by 50.8 µm, 75 µm by 75 µm or 85 µm by 85 µm.

According to the embodiment illustrated in , the device 1 comprises a second optical filter 39, located on the upper face of the first optical filter 18, more precisely on the upper face of the layer 35. For example, the optical filter 39 is in contact with the upper face of layer 35.

Alternatively, the optical filter 39 is located between the image sensor 11 and the angular filter 18 or between two layers constituting the angular filter 18, for example, between the layer 23 and the substrate 31.

The optical filter 39 is different from the optical filter 18, that is to say, they are two structures of different composition and function.

The optical filter 39 comprises a plurality of elementary filter patterns 41 regularly distributed over the surface of the sensor. Within the optical filter 39, the filter patterns 41 are preferably all identical except for manufacturing differences. For example, the optical filter 39 is, apart from the filter patterns 41, transparent in the visible and infrared range. Alternatively, the optical filter 39 is, apart from the filter patterns 41, partially transparent in the visible and infrared range. For example, apart from the filter patterns 41, the optical filter 39 is made up of a single material having uniform or homogeneous optical properties. For example, apart from the filter patterns 41, the optical filter 39 is made of air, a partial vacuum or a polymer.

For example, the filter patterns 41 can correspond to a combination of several resins, for example colored resins, for example resins from the "COLOR MOSAIC" commercial range from the manufacturer Fujifilm.

Each filtering pattern 41 comprises at least two color filters 43. The color filters 43 within the same filtering pattern 41 are adjacent, that is to say that in the XZ plane, the filtering pattern 41 is uninterrupted and that each color filter 43 a, at least one edge in common with another color filter 43 of the same filter pattern 41.

For example, the color filters 43 all have a substantially square shape when viewed from above. For example, the color filters 43 within the same filter pattern 41 all have substantially the same shape and the same lateral dimensions. Each color filter 43 has, for example, an area (in the XZ plane) corresponding to the area of at least one submatrix of two by two adjacent pixels 37. In other words, the color filters 43 have, for example a dimension, along the X axis, corresponding to at least twice the dimension of a pixel 37 and a dimension, in the direction of the Z axis, corresponding at least twice the dimension, along the Z axis, of a pixel 37.

An advantage of these dimensions is that the step of transferring or forming the optical filter 39 on the upper face of the angular filter 18 then does not require alignment of the optical filter 39 and the filter patterns 41 with the photodetectors 21. Indeed , by sizing the color filters 43 in this way, it is ensured that each color filter 43 completely covers at least one pixel 37 and more precisely a photodetector 21, even without prior alignment of the two structures concerned.

For example, the filter pattern 41 comprises at least one color filter 43ir called an infrared filter, adapted to allow only infrared radiation to pass, that is to say to block all wavelengths outside the 700 nm band. at 1 mm, preferably outside the band from 700 nm to 1100 nm. The 43ir color filters make it possible, for example, to measure stray radiation in order to take it into account in the results obtained for the identification of a fake finger.

For example, the filter pattern 41 comprises at least one color filter 43v, called a visible filter, adapted to allow only infrared radiation and a restricted range of wavelengths in the visible, for example only infrared radiation and green or only infrared and blue radiation or only infrared and red radiation.

For example, the material constituting the optical filter 39 apart from the filter patterns 41, for example a resin or a polymer material, for example transparent, is first deposited on the entire upper face of the optical filter 18 , more particularly, on the upper face of the layer 35. At this stage, this material forms a layer extending continuously and with a substantially uniform thickness over the entire upper surface of the optical filter 18. This material is then, by example, removed locally by photolithography or photolithogravure so as to form housings intended to receive a first part of the color filters 43 of the filter patterns 41 corresponding to all of the color filters 43 of the same type, that is to say the color filters 43 having the same filtering properties. Still as an example, the material constituting the color filters 43 considered is deposited in full plate on the upper face of the structure and more precisely on the upper face of the optical filter 39 and in the housings previously formed in this filter 39. The upper face of the layer of the material constituting the first part of the color filters 43 then undergoes mechanical-chemical planarization (CMP, Chemical Mechanical Planarization) so as to reveal the upper face of the optical filter 39 or photolithography so as to remove the material constituting the color filters 43 considered, located on the surface of the optical filter 39. For example, the steps of formation, filling of the housings and unveiling by CMP or lithography are repeated for all types of color filters. According to one embodiment, the thickness of the color filters is between 200 nm and 10 µm, preferably between 500 nm and 2 µm.

Alternatively, the color filters 43 and the material constituting the optical filter 39, apart from the patterns 41, are deposited locally on the surface of the angular filter 18 by localized deposition techniques such as the screen printing technique, the jet technique. ink (inkjet) or the spray technique (spray).

Different arrangements of color filters 43 within a filter pattern 41 and different arrangements of filter patterns 41 within the optical filter 39 are detailed below in relation to Figures 2 to 4.

There represents, in a partial and schematic top view, an embodiment of the device 1 for acquiring images of the , there being a sectional view, according to sectional plane AA of the .

In the example of the , a filter pattern 41 includes four color filters 43.

1. un filtre couleur 43ir est adapté à bloquer l'ensemble des longueurs d'ondes hors du domaine de l'infrarouge ; et
2. trois filtres couleurs 43v sont chacun adapté à ne laisser passer que l'infrarouge et au moins une longueur d'onde ou gamme de longueurs d'ondes dans le visible.

In the example of the , among the color filters 43:

1. a 43ir color filter is adapted to block all wavelengths outside the infrared range; And
2. three 43v color filters are each adapted to allow only infrared and at least one wavelength or range of wavelengths in the visible to pass.

In the example of the , 43v color filters are all different, that is to say they are not suitable for passing the same wavelength or range of wavelengths in the visible.

1. le filtre couleur 43ir (IR) dit filtre infrarouge adapté à bloquer toutes les longueurs d'ondes hors de la bande de 700 nm à 1 mm, de préférence, hors de la bande de 700 nm à 1100 nm ;
2. un filtre couleur 43r (R) dit filtre rouge adapté à laisser uniquement les longueurs d'ondes de l'infrarouge et au moins une longueur d'onde de la bande du rouge, c'est-à-dire la bande comprise entre 600 nm et 700 nm ;
3. un filtre couleur 43b (B) dit filtre bleu adapté à laisser uniquement les longueurs d'ondes de l'infrarouge et au moins une longueur d'onde de la bande du bleu, c'est-à-dire la bande comprise entre 430 nm et 490 nm ; et
4. un filtre couleur 43g (G) dit filtre vert adapté à laisser uniquement les longueurs d'ondes de l'infrarouge et au moins une longueur d'onde de la bande du vert, c'est-à-dire la bande comprise entre 510 nm et 570 nm.

By way of example, the filter pattern 41 of the understand :

1. the 43ir color filter (IR) called infrared filter adapted to block all wavelengths outside the band from 700 nm to 1 mm, preferably outside the band from 700 nm to 1100 nm;
2. a color filter 43r (R) called red filter adapted to allow only infrared wavelengths and at least one wavelength of the red band, that is to say the band between 600 nm and 700 nm;
3. a color filter 43b (B) called a blue filter adapted to allow only infrared wavelengths and at least one wavelength of the blue band, that is to say the band between 430 nm and 490 nm; And
4. a 43g color filter (G) called green filter adapted to leave only the infrared wavelengths and at least one wavelength of the green band, that is to say the band between 510 nm and 570nm.

In the example of the , the color filters 43 are arranged in a “T” (inverted in the orientation of the ) so that the infrared filter 43ir has a common side with the red filter 43r, a common side with the blue filter 43b and a common side with the green filter 43g. For example, the color filters 43g and 43b are separated by the infrared filter 43ir. In other words, the filter pattern 41 as illustrated in comprises, along the Z axis, in order, the green filter 43g, the infrared filter 43ir and the blue filter 43b and along the X axis, the infrared filter 43ir and the red filter 43r.

Alternatively, the filters 43 can be arranged within the "T" of the filter pattern 41 differently from what has been described above.

By way of example, the elementary filter patterns 41 are arranged in a plurality of interlaced matrices, each matrix comprising lines parallel to the direction of the lines of the matrix of photodetectors 21 and columns parallel to the direction of the columns of the matrix of photodetectors 21. In this example, in each matrix, two consecutive filter patterns 41 of the same row are spaced by the same distance Pz, and two consecutive filter patterns 41 of the same column are spaced by the same distance Px. In other words, in this example, the elementary filter patterns 41 are arranged according to several interlaced matrices with the same pitches in the X direction and in the Z direction.

The successive matrices of filter patterns 41 are interleaved with a constant offset δx from a matrix to its nearest neighbor in the direction X and a constant offset δz from a matrix to its nearest neighbor in the direction Z. example, any two consecutive rows of filter patterns 41 of the optical filter 39 are spaced by the same distance Ex and any two consecutive columns of filter patterns 41 of the optical filter 39 are spaced by the same distance Ez. For example, the filter patterns 41 are arranged according to at least two interlaced matrices with an offset in X and Z between two successive matrices. In the example illustrated in , the filter patterns 41 are arranged according to three interlaced matrices with an offset in X and Z between two successive matrices.

By way of example, along the axis the dimension of six pixels 37 and the dimension of ten pixels 37. Similarly, along the Z axis, the distance Pz is between the dimension of six pixels and the dimension of twenty pixels 37, for example greater than the dimension of eight pixels 37 and for example between the dimension of nine pixels 37 and the dimension of fourteen pixels 37.

For example, the offset δx is greater than the dimension, along the X axis, of six pixels 37 and the offset δz is greater than the dimension, along the Z axis, of eight pixels 37. The distance Ex is , for example, greater than the dimension, along the ensure that lines of underlying photodetectors 21 are completely not covered by filter patterns 41, and, similarly, that columns of underlying photodetectors 21 are completely not covered by patterns 41.

An advantage of entire rows and columns of photodetectors 21 not being covered by color filters 43 is that this facilitates image processing and in particular improves fingerprint detection and identification performance.

There represents, in a partial and schematic top view, another embodiment of the image acquisition device of the . More particularly, the differs from the in that the color filters 43 are arranged within the filter pattern 41 so that the filter pattern 41 has a square shape.

Each filter pattern 41 of the optical filter 39 of Fig. 3 comprises the same color filters 43 as those present in the filter pattern 41 of the optical filter 39 of the . Each filter pattern 41 of the optical filter of the thus includes a 43ir infrared filter, a 43b blue filter, a 43r red filter and a 43g green filter.

By way of example, within a filter pattern 41, as illustrated in , the filters 43ir and 43b are opposed and the filters 43r and 43g are opposed. For example, in the orientation of the , each filter pattern 41 includes, in its upper left corner, the blue filter 43b.

For example, along the X axis, the distance Px is between the dimension of four pixels 37 and the dimension of twenty-one pixels 37 of the device, for example greater than the dimension of five pixels 37 and for example example between the dimension of six pixels 37 and the dimension of ten pixels 37. Due to the square shape of the filter patterns 43 illustrated in , the dimensions described above for the distance Px also apply for the distance Py.

For example, the offsets δx and δz are greater than the dimension, respectively along the X axis and along the Z axis, by six pixels 37. The distances Ex and Ez are, for example, greater than the dimension, respectively along the X axis and along the Z axis, of two pixels 37.

There represents, in a partial and schematic top view, another embodiment of the image acquisition device of the . More particularly, the differs from the in that the filter patterns 41 only include two of the three color filters 43r, 43b and 43g.

In the example of the , only the 43g and 43r color filters are present in addition to the 43ir filter. As a variant, the two color filters can be color filters 43g and 43b, or 43b and 43r.

The dimensions of the color filters 43, the arrangement of the patterns 41 within the optical filter 39 and the spacing between the patterns 41 are, for example similar to what was described above for the device presented in the .

There represents, through a partial and schematic perspective view, an embodiment of the device for acquiring images of the .

In , device 1 has been simplified. The image sensor 11 and the angular filter 18 are represented by a single white parallelepiped.

The particularity of this embodiment is that the infrared filter 43ir is not made up of a specific filtering material different from the visible filters 43v, but is formed by superposition of the constituent materials of at least two of the visible filters 43v of the pattern 41 .

For example, during the formation of the optical filter 39, the color filters 43b, 43r and/or 43g are deposited one after the other so that they partly overlap. In this embodiment the color filters 43r, 43g and 43b each have an area equivalent to the area of eight pixels 37, that is to say that each color filter 43r, 43g and/or 43b has an area corresponding to the area area of two pixels 37 by four pixels. For example, filters 43r, 43g and/or 43b overlap on half of their surfaces. For example, the filters 43r, 43g and 43b are superimposed so that, in top view, the pattern 41 formed by the filters 43r, 43g and 43b corresponds to the pattern 41 illustrated in , 3 or 4.

In , the 43ir infrared filter corresponds to the superposition of the three color filters 43r, 43g and 43b.

1. le filtre rouge 43r a une largeur, selon l'axe Z, correspondant à la largeur, selon l'axe Z, de deux pixels et une longueur, selon l'axe X, correspondant à la longueur, selon l'axe X, de quatre pixels 37 ;
2. le filtre bleu 43b a une largeur, selon l'axe Z, correspondant à la largeur, selon l'axe Z, de quatre pixels et une longueur, selon l'axe X, correspondant à la longueur, selon l'axe X, de deux pixels 37 ; et
3. le filtre vert 43g a une largeur, selon l'axe Z, correspondant à la largeur, selon l'axe Z, de quatre pixels et une longueur, selon l'axe X, correspondant à la longueur, selon l'axe X, de deux pixels 37.

In the example of the :

1. the red filter 43r has a width, along the Z axis, corresponding to the width, along the Z axis, of two pixels and a length, along the X axis, corresponding to the length, along the X axis, of four pixels 37;
2. the blue filter 43b has a width, along the Z axis, corresponding to the width, along the Z axis, of four pixels and a length, along the X axis, corresponding to the length, along the X axis, of two pixels 37; And
3. the green filter 43g has a width, along the Z axis, corresponding to the width, along the Z axis, of four pixels and a length, along the X axis, corresponding to the length, along the X axis, of two pixels 37.

An advantage of the embodiments described lies in the fact that the color filters 43 of the same elementary filter pattern 41 are next to each other. This makes it possible to reduce the number of pixels 37 only partially covered by a color filter 43. In fact, each color filter 43, having an area corresponding to the area of four pixels 37, completely covers at least one photodetector 21 whose received signal can be exploited and can partially cover up to eight neighboring photodetectors 21 (see the example of the ) whose signal will then be difficult or even impossible to use to reconstruct a fingerprint or identify a user. Placing the color filters 43 together makes it possible to limit the total number of partially covered photodetectors 21 on the scale of the optical filter 39.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to those skilled in the art.

In particular, the embodiment illustrated in is compatible with the embodiments of Figures 3 and 4.

Furthermore, in the embodiments described, the optical filter 18 corresponds to an angular filter. However, they can be applied to devices not comprising an optical filter 18, comprising another type of optical filter, such as a spatial filter or comprising an angular filter different from that shown in .

In addition, the embodiments described can be applied to devices whose photodetectors and/or pixels have geometries different from what has been described.

Again, the embodiments described are not limited to the examples of materials and dimensions mentioned in the present description.

Finally, in the embodiments described, the filter patterns 41 are organized within the optical filter 39 according to several interlaced matrices and offset with respect to each other in the directions X and Z. The embodiments described are not, however, limited not in this particular case.

Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art based on the functional indications given above.

Claims (14)

Optical filter (39) intended to cover a matrix of photodetectors (21), the optical filter comprising a plurality of identical elementary filter patterns (41) regularly distributed over the surface of the optical filter (39), each filter pattern (41) comprising a arrangement of at least two color filters (43, 43v, 43ir, 43r, 43b, 43g) joined together, two neighboring elementary filter patterns (41) being spaced apart by the size of at least two photodetectors. Optical filter (39) according to claim 1, in which each color filter (43, 43v, 43ir, 43r, 43b, 43g) has an area corresponding to the area of at least one sub-matrix of two by two photodetectors (21 ) adjacent. Optical filter according to claim 1 or 2, in which two filter patterns (41) are spaced apart by the dimension of at least four photodetectors (21) in the direction (Z) of the lines of the matrix and by the dimension of at least four photodetectors in the direction (X) of the columns of the matrix. Optical filter according to any one of claims 1 to 3, wherein the filter patterns (41) are positioned within the optical filter (39) such that areas extending over the entire length or width of the optical filter are not covered by the filter patterns, the zones having a width equal to the width of at least two photodetectors (21). Optical filter according to any one of claims 1 to 4, in which the filter patterns (41) comprise at least three color filters (43, 43v, 43ir, 43r, 43b, 43g) joined together, at least one (43ir) at least three color filters corresponding to a superposition of the other color filters. Optical filter according to claim 5, wherein each of said other color filters (43v, 43r, 43b, 43g) passes a wavelength band of visible radiation and infrared radiation. Optical filter according to claim 5 or 6, in which said (43ir) at least one of the at least three color filters allows only infrared radiation to pass. Optical filter according to any one of claims 1 to 7, in which each filter pattern (41) comprises three color filters (43, 43v, 43ir, 43r, 43b, 43g) arranged in an "L". Optical filter according to any one of claims 1 to 7, in which each filter pattern (41) comprises four color filters (43, 43v, 43ir, 43r, 43b, 43g) arranged in a square. Optical filter according to any one of claims 1 to 7, in which each filter pattern (41) comprises four color filters (43, 43v, 43ir, 43r, 43b, 43g) arranged in a "T". Image acquisition device (1) comprising a sensor (11) with photodetectors (21) and an optical filter (39) according to any one of claims 1 to 10. Image acquisition device according to claim 11, wherein the photodetectors (21) are organic. Image acquisition device according to claim 11 or 12, comprising an angular filter (18), different from the optical filter (39). Image acquisition device according to any one of claims 11 to 13, comprising a processing unit (19).