PIXEL UNIT HAVING INFRARED ABSORBER, PIXEL ARRAY, AND CAMERA EMBODIMENT WITH SUCH PIXEL ARRAY - Patent application

Abstract

A back-illuminated pixel including a photodiode (301) and an infrared absorber (301) having embedded nanostructures (402, 403), wherein the infrared absorber (301) having embedded nanostructures (401, 402) is configured to absorb light (305) passing through the photodiode (301).

Description

[Technical field]

[0001] The present disclosure relates generally to the field of imaging sensors, and more particularly to cameras and electronic devices that use such sensors. [Background technology]

[0002] Imaging sensor pixels are usually based on semiconductor technology. In semiconductors, the excitation of an electron from the valence band to the conduction band creates free charge carriers such as electron-hole pairs. This excitation leaves a hole in the valence band that behaves as a positive charge, creating an electron-hole pair. The hole (i.e. the positive charge) moves towards the anode connection of the circuit, while the excited electron is attracted to the cathode connection. This is how a photocurrent is generated.

[0003] Unconverted light incident on a photodiode can cause reflections that create undesirable artifacts, such as crosstalk, in adjacent pixels.

[0004] Therefore, it is generally desirable to reduce artifacts and improve the response of pixels to incident light as much as possible. Summary of the Invention [Means for solving the problem]

[0005] According to a first aspect, the present disclosure provides a back-illuminated pixel including a photodiode and a nanostructured embedded infrared absorber, the nanostructured embedded infrared absorber configured to absorb light passing through the photodiode.

[0006] According to a further aspect, the present disclosure provides a sensor device including a pixel array, the pixel array including a plurality of back-illuminated pixels as described above.

[0007] According to a further aspect, the present disclosure provides a ToF camera including a sensor device as described above.

[0008] Further aspects are set out in the dependent claims, the following description and the drawings, in which: Embodiments are described by way of example with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0009] [Figure 1] 1 shows a schematic cross-sectional view of a back-illuminated IR pixel with metallization layers and logic in the xz plane. [Diagram 2] 1 shows a schematic cross-sectional view of a back-illuminated IR pixel having a metallization layer, logic, and an infrared absorbing layer in the xz plane. [Diagram 3] 1 shows a schematic cross-sectional view in the xz plane of a back-illuminated IR pixel having a nanostructured metallization layer and an infrared absorbing layer. [Figure 4] 1 shows a schematic diagram of the arrangement of nanostructures in a nanostructure array having a periodic cell structure in a top view in the xz plane. [Diagram 5] An example of an infrared absorber with ellipsoidally shaped nanostructures embedded in an array with a periodic cell structure, which may be configured in the back-illuminated pixel of FIG. 3, is shown diagrammatically in a top view in the xz plane. [Figure 6] A cell of the nanostructure array of FIG. 5 is shown diagrammatically in a top view in the xz plane (see 504 in FIG. 5). [Figure 7] FIG. 7 shows a schematic front view of the nanostructured cell of FIG. 6 in the xz plane. [Figure 8] A back-illuminated pixel having a metallization layer, an infrared absorbing layer embedded with nanostructures, and a filled trench isolation (FTI) at the border with adjacent pixels is shown diagrammatically in a cross-sectional view in the xz plane. [Figure 9] A back-illuminated pixel with a metallization layer, an infrared absorbing layer embedded with nanostructures, and deep trench isolation (DTI) at the border with adjacent pixels is shown diagrammatically in a cross-sectional view in the xz plane. [Figure 10]FIG. 2 shows a schematic diagram of a back-illuminated pixel array structure with an additional IR absorber disposed above the photodiode array in a cross-sectional view in the xz plane. [Figure 11] The structure of the back-illuminated pixel array of FIG. 10 is shown diagrammatically in a top view in the xz plane. [Figure 12A] 1 shows an exemplary configuration of an infrared absorber with embedded nanostructures optimized for absorption at a wavelength of 940 nm. [Figure 12B] A contour plot of the relative reflected power density at a transverse cut plane located 240 nm above the inserted nanostructures is shown for the configuration of FIG. 12A (240 nm t2 SiO2). [Figure 13A] 1 shows an exemplary configuration of a nanostructure-embedded infrared absorber optimized for absorption at a wavelength of 1380 nm. [Figure 13B] A contour plot of the relative reflected power density at a transverse cut plane located 190 nm above the inserted nanostructures is shown for the configuration of FIG. 13A (190 nm t2 SiO2). [Figure 14A] 1 shows an exemplary configuration of a nanostructure-embedded infrared absorber optimized for absorption at a wavelength of 1550 nm. [Figure 14B] A contour plot of the relative reflected power density at a transverse cut plane located 190 nm above the inserted nanostructures is shown for the configuration of FIG. 14A (190 nm t2 SiO2). [Figure 15] The performance of the nanostructured IR absorbers described in the above embodiments is illustrated in an absorption vs. wavelength diagram. [Figure 16] The band of minimum absorption (WMA) is shown as explained with respect to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Before proceeding to a detailed description of the embodiments with reference to the figures, some general remarks will be made.

[0011] Embodiments disclose a back-illuminated pixel that includes a photodiode and a nanostructure-embedded infrared absorber, where the nanostructure-embedded infrared absorber is configured to absorb light passing through the photodiode.

[0012] Back-illuminated pixels may be applied, for example, in IR imaging, IR time-of-flight (ToF), and IR sensing.

[0013] For example, including nanostructures on top of the metallization layer of a back-illuminated pixel can avoid reflection of infrared (IR) light at the metallization layer, thereby preventing undesirable effects such as crosstalk. Nanostructure-embedded infrared absorbers can be particularly useful for infrared imaging or ToF (time-of-flight) pixels. However, they can also be used for other sensing pixels where leaking infrared light can result in undesirable side effects (e.g., crosstalk).

[0014] The infrared absorber with embedded nanostructures can be composed of metamaterials designed to have light absorbing properties not found in naturally occurring materials. Metamaterials can be a collection of structures made from composite materials with different electromagnetic properties, e.g., metals, semiconductors, and / or dielectrics. The infrared absorber of the embodiment is a metamaterial. Metamaterials can be a combination of different materials formed, for example, by layers and / or structures, resulting in a "new" material with properties not found in nature.

[0015] According to some embodiments, the embedded nanostructures provide a light absorbing metasurface.

[0016] The infrared absorber may have a multi-layer structure including a first layer and a second layer disposed below the first layer, and the nanostructures are embedded in the first layer of the multi-layer structure.

[0017] In some embodiments, the infrared absorber consists of two layers of material and intercalated nanostructures, the combination of the layers and nanostructures resulting in a metasurface with absorbing properties.

[0018] According to some embodiments, the first layer is made of material A, the second layer is made of material B that is different from material A, and the nanostructures embedded in the first layer are made of the same material as the second layer.

[0019] Embedding nanostructured cells in a layer of material A, followed by a second layer of material B, allows for resonance that absorbs the desired wavelength.

[0020] Material A is, for example, a dielectric material, and material B is, for example, a metal.

[0021] That is, according to some embodiments, the nanostructures are embedded in a dielectric layer, and the nanostructures embedded in the dielectric layer together with the metal layer represent an absorber, i.e., the dielectric layer, the interposed nanostructures and the metal layer form an absorber (e.g., an absorber metasurface).

[0022] According to some embodiments, material A is silicon dioxide and material B is aluminum.

[0023] The embedded nanostructures can be organized as a nanostructure array having a spatially repeating pattern.

[0024] Metamaterials are typically arranged in repeating patterns on scales smaller than the wavelength of the phenomena they affect.

[0025] The nanostructure array can be structured, for example, as a repeating cell. Such a periodic structure can provide uniform absorption properties.

[0026] For example, in embodiments, two materials (eg, dielectric+metal) can be used to create a multi-layer structure with a spatially repeated pattern with a predefined cell period.

[0027] The repetition of cells can, for example, impart symmetrical properties to the nanostructure array.

[0028] According to some embodiments, the cell period of the nanostructure array is independent of the pixel pitch (i.e., does not necessarily coincide with the pixel pitch). Independence from pixel dimensions can be achieved, for example, by providing an absorber with uniform performance across its surface.

[0029] The nanostructure array may include spatially repeated structures.

[0030] In this way, by combining layers of different materials with intercalated nanostructure arrays, metamaterials can be created that derive their properties not only from the properties of the base material itself, but also from the designed structures.

[0031] For example, the shape, geometry, size, orientation and arrangement of the structures can provide metamaterials with properties that allow them to manipulate electromagnetic waves, in particular to absorb or block predefined wavelengths or wavelength ranges. That is, by selecting these properties, the absorber can be tailored to optimize absorption of a particular infrared bandwidth. Also, different combinations of material layers and nanostructures can be used to optimize absorption of a particular infrared bandwidth. An optimized combination of material properties, nanostructures and dimensions can optimize the performance of the absorber. Optimizing the resonances can achieve a desired bandwidth of absorption even when the dimensions of the structures are varied over a range, e.g., due to typical variations during the manufacturing process.

[0032] The structures of the nanostructure array can be located, for example, at cell boundaries.

[0033] According to some embodiments, the structures of the nanostructure array change their orientation in each row of the pattern.

[0034] For example, the structures of a nanostructure array can include horizontally positioned structures and vertically positioned structures.

[0035] The structures of the nanostructure array can have an elliptical or quasi-circular shape.

[0036] Inserting a quasi-circular structure in a layer of material A, followed by a layer of material B, results in a resonance that absorbs the desired wavelength.

[0037] The elliptical or semi-circular shape may be defined, for example, by a minor diameter and a major diameter.

[0038] The infrared absorber with nanostructures may be located, for example, on top of a metallization layer, and the infrared absorber layer with embedded nanostructures can prevent light from reaching the metallization layer. The nanostructures can be integrated, for example, on top of the metallization layer of existing pixel designs to improve pixel performance.

[0039] The infrared absorber may be configured to absorb light with central wavelengths of around 940 nm, 1380 nm, and 1550 nm, for example.

[0040] According to some embodiments, the backside illuminated pixels include filled trench isolation at the boundaries with adjacent pixels.

[0041] According to some embodiments, the backside illuminated pixels include deep trench isolation at the boundaries with adjacent pixels.

[0042] The embodiments also disclose a sensor device including a pixel array, the pixel array comprising a plurality of pixels as defined herein. For example, the sensor device may include a photodiode array having a plurality of back-illuminated pixels as defined herein. The sensor device may be, for example, a semiconductor detector that measures the effect of incident photons.

[0043] The photodiode array may, for example, comprise an additional IR absorber disposed above the photodiode array as presented in the present invention. This configuration may be used to form a mask in areas of the sensor where it is desired to avoid the transmission of IR light in those areas.

[0044] An additional IR absorber disposed above the photodiode array may be configured to provide the functionality of an anti-flare shield and / or an on-pixel barrier shield.

[0045] The present embodiment also discloses a camera device comprising a sensor device having a back-illuminated pixel as described herein. The camera may be, for example, an IR imaging camera or a range imaging camera such as a time-of-flight camera (ToF camera). However, the camera may also be another imaging camera such as an active pixel camera (APS) that benefits from avoiding IR crosstalk.

[0046] Back-illuminated pixels The sensor according to these embodiments comprises a pixel array including a plurality of back-illuminated pixels, such as the back-illuminated IR pixels described with respect to FIGS. 1 and 2 below.

[0047] FIG. 1 shows a schematic cross-sectional view of a back-illuminated IR pixel with metallization layers and logic in the xz plane. Broadband infrared (IR) light 100 incident along the z direction is filtered by an IR bandpass filter 101, so that only light of a desired wavelength passes through the IR bandpass filter 101. This filtered light 102 illuminates a back-illuminated pixel 103. The back-illuminated pixel 103 includes a photodiode 104, a metallization layer 105, and logic 108. The filtered light 102 is incident on the photodiode 104, which converts a portion of the filtered light 102 into a photocurrent. Unconverted light 106 in the photodiode 104 impinges on the metallization layer 105, resulting in reflections 107. These reflections 107 may contain a substantial portion of the unconverted light 106, which may cause crosstalk with adjacent pixels and produce undesirable artifacts in those adjacent pixels.

[0048] Back-illuminated pixels with infrared absorbers FIG. 2 shows a schematic cross-sectional view of a back-illuminated IR pixel with a metallization layer, logic, and an infrared absorbing layer in the xz plane. Broadband IR light 100 incident along the z direction is filtered by an IR bandpass filter 101, allowing only light of a desired wavelength to pass through the IR bandpass filter 101. This filtered light 102 illuminates a back-illuminated pixel 200. The double arrow represents the pixel pitch. The back-illuminated pixel 200 includes a photodiode 104, an infrared absorber 201, a metallization layer 105, and logic 202. The infrared absorber 201 may be, for example, an infrared absorber layer. The filtered light 102 is incident on the photodiode 104, which converts a portion of the filtered light 102 into a photocurrent. The unconverted light 203 in the photodiode 104 strikes the infrared absorber 201, resulting in a reflection 204. The reflection 204 may include a substantial portion of the unconverted light 203. The reflection 204 may cause crosstalk with adjacent pixels, thereby causing undesirable artifacts in those adjacent pixels. However, the reflection 204 may be reduced compared to the reflection (see 107 in FIG. 1) that occurs in the back-illuminated pixel of FIG. 1 (see 103 in FIG. 1) that does not include an infrared absorber.

[0049] Back-illuminated pixels with infrared absorber metasurfaces FIG. 3 shows a schematic cross-sectional view in the xz plane of a back-illuminated IR pixel having a metallization layer and a nanostructure-embedded infrared absorbing layer. Broadband IR light 100 is filtered by an IR bandpass filter 101, allowing only light of a desired wavelength to pass through the IR bandpass filter 101. The filtered light 102 illuminates a back-illuminated pixel 300. The back-illuminated pixel 300 includes a photodiode 301, an infrared absorber 302, a metallization layer 303, and logic 304. The filtered light 102 enters the photodiode 301, which converts a portion of the filtered light 102 into an electric current. Unconverted light 305 in the photodiode 301 impinges on the nanostructure-embedded infrared absorber 302, resulting in a reflection 306 of a significant portion of the unconverted light. The double arrow represents the pixel pitch.

[0050] In the embodiment of FIG. 3, the infrared absorber 302 includes an infrared absorber layer with embedded nanostructures (e.g., the infrared absorber layer with embedded nanostructures forms a metasurface). The infrared absorber with embedded nanostructures functions as an infrared absorber metasurface. The infrared absorber with embedded nanostructures 302 prevents most of the light 305 from reaching the metallization layer 303 of the pixel, avoiding reflections that may cause undesirable effects such as crosstalk. As a result of applying the infrared absorber layer with embedded nanostructures, the reflection 306 may be significantly reduced compared to the reflection (see 107 in FIG. 1) that occurs in the back-illuminated pixel of FIGS. 1 and 2 (see 103 in FIG. 1 and 200 in FIG. 2).

[0051] The infrared absorber 301 may be configured to absorb light of wavelengths of, for example, 940 nm, or 1380 nm, or 1550 nm.

[0052] FIG. 4 shows a schematic representation in a top view in the xz plane of a nanostructure array with a periodic cell structure used in the infrared absorber of the back-illuminated pixel of FIG. 3. The nanostructure array 403 comprises structures 401, 402 with a quasi-circular shape. The nanostructure array 403 has a periodic cell structure. The layer comprising the nanostructure array 403 is made of two different materials, for example material A and material B, and has a spatially repeated pattern. The nanostructures 404 comprise structures 401, 402 made of material B. The nanostructures 404 are embedded in a first layer (701 in FIG. 7) of an infrared absorber (302 in FIG. 3) according to a periodic pattern. The two materials used may be, for example, a metal, for example aluminum, as material B and a dielectric, for example silicon dioxide (SiO2), as material A.

[0053] Nanostructure array 403 is structured in the x and y directions as 4x4 repeating secondary cells 404, with each secondary cell 404 having a diameter d. That is, nanostructure cells 404 have a cell period d. The repetition of cells in the x and y directions gives nanostructure array 403 a symmetrical property. Structures 401, 402 are positioned such that their axes are perpendicular to the boundaries of cell 404. Each structure 401, 402 is quasi-circular and has two dimensions a, b. Dimension a relates to the minor diameter of the feature (i.e., relates to the minor axis). Dimension b relates to the major diameter of the feature (i.e., relates to the major axis).

[0054] The larger axis (major axis) of the ellipse, b, determines the frequency at which the nanostructure has a high absorption peak, and the smaller axis (minor axis) of the ellipse, a, determines the frequency at which the absorption is low.

[0055] The distance between the centers of two adjacent structures 402 in the same row is equal to the cell period d, and the distance between the centers of two adjacent structures 402 in the same column is also equal to the cell period d. The dashed grid represents the spatial periodicity d of the nanostructured cells 404. Such a periodic structure may provide homogeneous absorption properties. Increasing the periodicity d increases the valleys between the absorption peaks.

[0056] Note that the cell period d is independent of the pixel pitch, i.e., it does not necessarily coincide with the pixel pitch.

[0057] Optimized absorption can be achieved by an optimized combination of material properties and dimensions. The absorber layer with embedded nanostructure arrays described above can absorb most of the IR light (305 in FIG. 3) before it reaches the metallization layer (see 303 in FIG. 3). In particular, the nanostructure-embedded absorber can be tailored to optimize absorption of specific infrared bandwidths and use different combinations of materials A and B.

[0058] FIG. 5 shows a schematic representation of a nanostructure array having the periodic cell structure of FIG. 4 with exaggerated dimensions. Nanostructure array 403 includes structures 401, 402 having an elliptical shape. Nanostructure array 403 is structured as 4×4 repeating secondary cells 404 in the x and y directions, with each secondary cell 404 having a diameter d. That is, nanostructure cells 404 (i.e., structural cells) have a cell period d. The repetition of cells in the x and y directions gives the array a symmetrical property. Each elliptical shaped structure 401, 402 has two dimensions a, b. Dimension a relates to the minor diameter of the elliptical shape (i.e., the minor axis of the ellipse). Dimension b relates to the major diameter of the elliptical shape (i.e., the major axis of the ellipse). The ratio of dimensions a and b is exaggerated in FIG. 5 to make the difference more clear.

[0059] The elliptical structures 401, 402 are positioned such that their axes are perpendicular to the boundaries of the cells 404. In other words, the elliptical structures 401, 402 are positioned on the boundaries of the cells 404 oriented along the x and y directions. Thus, each nanostructured cell 404 contains two vertically positioned halves of the structures 402 and two horizontally positioned halves of the structures 401, and the two adjacent nanostructured cells 404 form the whole structure 401, 402.

[0060] The structures 401, 402 of the nanostructure array 403 change orientation in each column. Thus, in one row, dimension a (the minor axis of the ellipse) is parallel to the x-axis (vertically positioned structures 402), and in the next row, dimension a (the minor axis of the ellipse) is parallel to the y-axis (horizontally positioned structures 401). Thus, the structures 401, 402 include horizontally positioned structures 401 and vertically positioned structures 402.

[0061] The distance between the centers of two vertically adjacent structures 402 is equal to the cell period d, and the distance between two vertically adjacent structures 402 is e, where e=da. The distance in the x direction between two horizontally adjacent nanostructures 401 is f, where f=db. The distance between one vertically adjacent structure 402 and one adjacent horizontally adjacent nanostructure 401 is g.

[0062] Figure 6 shows a schematic representation of a cell of the nanostructure array of Figure 5 (see 404 in Figures 4 and 5) in a top view in the xz plane. The nanostructure cell 404 includes portions of structures 401, 402 (having an elliptical or quasi-circular shape, as shown in Figures 4 and 5 above) with two different dimensions a and b. The nanostructure cell 404 includes two halves of two vertically positioned structures 402 with diameters equal to b and a / 2, and two halves of two horizontally positioned nanostructures 401 with circle radii equal to a / 2 and b. The dimension of the nanostructure square cell 404 is equal to d.

[0063] Figure 7 shows a schematic front view of the nanostructured cell of Figure 6 in the xz plane. The nanostructured cell 404 has a multi-layer structure and includes two layers 701, 702, the second layer 702 being disposed below the first layer 701. The cell dimension is equal to d (independent of the pixel pitch). The first layer 701 is made of material A and the second layer 702 is made of material B. The second layer 702 made of material B has a thickness t a The first layer 701 has a thickness t bThe structure 402 is embedded (i.e. integrated) in the second layer 702. The structure 402 is made of material B, i.e. the same material as the second layer 702. The inserted structure 402 may have, for example, an elliptical or quasi-circular shape in the xz plane, as explained in Figures 3, 5 and 6 above.

[0064] The bottom surface of the insert structure 402 is disposed at a distance t 1 and the top surface of the insert structure 402 is located at a distance t 2 The first layer 701 with the embedded structure 402 forms an infrared absorber together with the second layer 702 (see 302 in FIG. 3). The thickness t 1 This determines the value of the absorption peak.

[0065] A layer 701 made of material A has embedded nanostructured cells, followed by a second layer 702 made of material B, allowing resonance to absorb the desired wavelengths.

[0066] By appropriate choice of composition, such multi-layer structures can be tuned to optimize absorption in specific infrared bandwidths.

[0067] In the embodiment of Figure 7, the material used in the original pixel may be used for the infrared absorber, however, it should be noted that in alternative embodiments, a different dielectric and a different metal layer, or two layers of different dielectrics may be used to create the infrared absorber metasurface.

[0068] Selecting the configuration may include, for example, selecting dimensions of the nanostructures (eg, a and b) and / or using different combinations of materials A and B.

[0069] For example, the nanostructures may use materials that have a low contamination probability for the fab and / or are readily available, designs that allow for simple and inexpensive manufacturing processes, and designs that are highly tolerant to dimensional variations during manufacturing. Such multi-layer structures can be easily integrated on top of metallization layers of existing pixel designs (such as metallization layer 303 in FIG. 3) and can improve pixel performance.

[0070] Backside illuminated pixels with added FTI or DTI FIG. 8 shows a schematic cross-sectional view in the xz plane of a back-illuminated pixel having a metallization layer, an infrared absorbing layer embedded with nanostructures, and a filled trench isolation (FTI) at the border with adjacent pixels. Similar to the back-illuminated pixel of FIG. 3, the broadband IR light 100 is filtered by an IR bandpass filter 101, so that only light of the desired wavelength passes through the IR bandpass filter 101. The filtered light 102 illuminates the back-illuminated pixel 800. The back-illuminated pixel 800, which includes a photodiode 301, is provided with a filled trench isolation (FTI) 801. The FTI is included in many pixel designs to reduce crosstalk and contributes independently to the infrared absorber function. The FTI 801 is formed between two adjacent photodiodes along two opposite sides of the photodiode 301, and thus between two adjacent pixels. The FTI 801 is a common barrier added to the pixel that may block crosstalk and may be independent of the infrared absorber. Similar to the back-illuminated pixel of FIG. 3, the back-illuminated pixel 800 further includes an infrared absorber 302 with embedded nanostructures, a metallization layer 303, and logic 304. The filtered light 102 is incident on the photodiode 301, which converts a portion of the filtered light 102 into a photocurrent. Unconverted light 305 in the photodiode 301 impinges on the infrared absorber 302 and produces a reflection 306. The infrared absorber 302 may include an infrared absorber layer with embedded nanostructures having an elliptical or quasi-circular shape, as shown with respect to FIGS. 4-7 above. In this manner, the infrared absorber 302 can largely prevent reflection 306 from penetrating into the metallization layer 303 and being reflected.

[0071] FIG. 9 shows a schematic cross-sectional view in the xz plane of a back-illuminated pixel with a metallization layer, an infrared absorbing layer embedded with nanostructures, and a deep trench isolation (DTI) at the border with adjacent pixels. As in FIG. 8, broadband IR light 100 is filtered by an IR bandpass filter 101, so that only light of a desired wavelength 102 passes through the IR bandpass filter 101. The filtered light 102 illuminates a back-illuminated pixel 900. The back-illuminated pixel 900 includes a photodiode 301 with a DTI 901. The DTI 801 is formed along two opposing sides of the photodiode 301, between two adjacent photodiodes, and thus between two adjacent pixels. The DTI 801 is included in many pixel designs to reduce crosstalk and contributes independently to the infrared absorber function. The DTI 801 is a common barrier added to pixels that blocks crosstalk and may be independent of the absorber. Similar to the back-illuminated pixel of FIG. 8, back-illuminated pixel 900 further includes an infrared absorber 302 with embedded nanostructures, a metallization layer 303, and logic 304.

[0072] Sensor with nanostructured IR absorber, anti-flare, OPB shield FIG. 10 shows a schematic cross-sectional view in the xz plane of the structure of a back-illuminated pixel array with an additional IR absorber disposed above the photodiode array. The back-illuminated pixel array 1000 includes a plurality of back-illuminated pixels with nanostructured IR absorbers, such as the back-illuminated pixels described with respect to FIGS. 3, 8 and 9 above. In particular, the back-illuminated pixel array 1000 includes a photodiode array layer 1002 (see also 301 in FIGS. 3, 8 and 9), an infrared absorber layer 1003 (see also 301 in FIGS. 3, 8 and 9), a metallization layer 1004 (see also 303 in FIGS. 3, 8 and 9), and a logic layer 1005 (see also 304 in FIGS. 3, 8 and 9). On top of the photodiode array layer 1002, an additional IR absorber 1001 is disposed, which has the same multi-layer structure as the IR absorber described with respect to FIGS. 4, 5, 6 and 7 above. As shown in Figure 11, this additional IR absorber 1001 covers only the outer area of ​​the back-illuminated pixel array 1000. An IR bandpass filter 1006 is located above the photodiode array and above the additional IR absorber 1001 (see also 101 in Figures 3, 8 and 9).

[0073] In the embodiment of FIG. 10, the additional IR absorber 1001 on top of the pixel provides the functions of anti-flare shield and on-pixel barrier (OPB) shield. The function of the anti-flare shield is to prevent undesired artifacts due to light blow (flare) in the image captured by the imaging sensor. Such light blow (flare) occurs when strong incident light hits some areas of the chip of the sensor, causing reflections at the surface of the chip and reflecting back into the optical stack, causing light to bounce and propagate across the sensor array. The function of the OPB is to prevent light from reaching unwanted areas of the chip, for example when it is desirable to separate the boundaries of the sensor array from outside chip reflections. Thus, the additional IR absorber 1001 on top of the pixel has the above-mentioned two functions: anti-flare (reflection) and OPB shield (transmission).

[0074] Figure 11 shows the structure of the back-illuminated pixel array of Figure 10 in a schematic top view in the xz plane. The top view of the ToF sensor structure (see 1000 in Figure 10a) shows a back-illuminated pixel array 1000 formed by a number of back-illuminated pixels. On top of a photodiode array layer 1002 formed by the photodiodes of the back-illuminated pixels, a nanostructured IR absorber layer 1001 is arranged. The nanostructured IR absorber layer 1001 has the same multi-layer structure as the IR absorber described with respect to Figures 4, 5, 6 and 7 above.

[0075] Design configuration example Figures 12A, 13A and 14A show three exemplary configurations of infrared absorbers with embedded nanostructures optimized for specific wavelengths. In each case, the nanostructures are configured as a nanostructure array with a cell period d. The nanostructure array is a set of structures with quasi-circular shapes located at the cell boundaries with varying orientations, as shown in Figures 4-7 above. The quasi-circular shapes correspond to elliptical shapes with two dimensions a (minor axis) and b (major axis) close to each other. The quasi-circular structures that make up the nanostructure array are made of aluminum. The layer in which the nanostructures are embedded is made of silicon dioxide (SiO2). The parameter t 1 SiO2 , t al , t 2 SiO2 , and t d defines the parameters of the layered structure. t 1 SiO2 (corresponding to t2 in FIG. 7) corresponds to the distance between the quasi-circular structure and the bottom surface of the silicon dioxide layer (701 in FIG. 7). 2 SiO2 (corresponding to t1 in FIG. 7) corresponds to the distance between the quasi-circular structure and the top surface of the silicon dioxide layer (701 in FIG. 7). d (t in Fig. 7 b t) corresponds to the thickness of the quasi-circular structure. al corresponds to the aluminum layer (702 in FIG. 7) located underneath the silicon dioxide layer (701 in FIG. 7) in which the nanostructures are embedded.

[0076] In general, the following dependencies are observed: The larger the axis b of the ellipse, the higher the frequency of the absorption peak. The smaller the axis a of the ellipse, the lower the frequency of the absorption peak. The periodicity of the nanostructure array (cell period d) increases the valleys between the peaks. The thickness of the layer between the ellipse and the lower aluminum plate t 2 SiO2 Determine the value of peak absorption.

[0077] 12A shows an exemplary configuration of an infrared absorber with embedded nanostructures optimized for absorption at a wavelength of 940 nm. The nanostructure configuration is shown in Table 1 below. [Table 1] Table 1: Nanostructure parameters optimized for absorption at 940 nm.

[0078] FIG. 12B shows the configuration of FIG. 12A (240 nm t 2 SiO2 12A ) at a transverse cut located 240 nm above the inserted nanostructure (layer number 5 in FIG. 12A ). The contour plots are plotted as a function of the incident power density [W / m 2 ] to reflected power density [W / m 2 ], with the ratio ranging from 0 to 1. Reflectance = Integral of relative reflected power density = 0.0123@#5(240nm t 2 SiO2 ) Absorption = 1 - Reflection = 0.9877@#5(240nm t 2 SiO2 ).

[0079] 13A shows an exemplary configuration of an infrared absorber with embedded nanostructures optimized for absorption at a wavelength of 1380 nm. The nanostructure configuration is shown in Table 2 below. [Table 2] Table 2: Nanostructure parameters optimized for absorption at 1380 nm.

[0080] FIG. 13B shows the structure of FIG. 13A (190 nm t 2 SiO2 13A ) at a transverse cut located 190 nm above the inserted nanostructure (layer number 5 in FIG. 13A ). The contour plots are plotted as a function of the incident power density [W / m 2 ] to reflected power density [W / m 2 ], with the ratio ranging from 0 to 1. Reflectance = Integral of relative reflected power density = 0.0161@#5(190nm t 2 SiO2 ) Absorption = 1 - Reflection = 0.9839@#5(190nm t 2 SiO2 )

[0081] 14A shows an exemplary configuration of an infrared absorber having nanostructures optimized for absorption at a wavelength of 1550 nm. The nanostructure configuration is shown in Table 3 below. [Table 3] Table 3: Nanostructure parameters optimized for absorption at 1550 nm.

[0082] FIG. 14B shows the structure of FIG. 14A (190 nm t 2 SiO2 14A ) at a transverse cut located 190 nm above the inserted nanostructure (layer number 5 in FIG. 14A ). The contour plots are plotted as a function of the incident power density [W / m 2 ] to reflected power density [W / m 2 ], where the ratio ranges from 0 to 1. Reflection = Integral of reflected power density = 0.0066@#5(190nm t 2 SiO2 ) Absorption = 1 - Reflectance = Relative 0.9934@#5(190nm t 2 SiO2 )

[0083] Figures 12B, 13B and 14B demonstrate that the proposed IR absorber designs have a uniform absorption capability over their entire area. This uniformity allows their use independent of the size and / or position of the structures underneath them, e.g., any pixel size and their position underneath the IR absorber can be chosen such that all pixels are similarly protected from crosstalk.

[0084] Table 4 below summarizes the designs for different frequencies. Table 4 provides the nominal geometric design parameters corresponding to a design variation coefficient of 0 nm, i.e., no variation from the nominal parameters. In addition, Table 4 also shows the results of a design variation of -10 nm and +10 nm in all horizontal dimensions simultaneously, i.e., the simultaneous variation of the dimensions represented in Figure 4. The absorption strength (referred to as the "power parameter" in Table 4) is provided in the form of a reference integral, which is the area on the absorption curve between ±25 nm of the absorber's central frequency (see Figure 17). This reference integral corresponds to a squared absorption of 2.5 (numerically 2.44). This reference integral represents the energy reflected by the absorber.

[0085] [Table 4] Table 4: Design summary for different frequencies

[0086] It should be noted that the dimensional variations shown in the above table are within a 10% range of the horizontal reference dimension, for example, +-10 nm ≦ 10% of the reference horizontal dimension.

[0087] FIG. 15 shows in a diagram the performance of a nanostructured IR absorber as described in the above embodiment. The horizontal axis of the diagram represents the wavelength λ of incident light in the range 600 nm to 1800 nm in nm, and the vertical axis represents the absorption of the IR absorber in the range 0.1 to 1 when incident light of wavelength λ hits the IR absorber. The solid curve shows the absorption for the nominal design parameters of Table 4 (factor 0 nm), reference integral value 1.4, central frequency CFA(l) 1586 nm, absorption A=0,999, and minimum absorption band WMA=137 nm. These parameters are the results of simulations, i.e., quantifying how superior the absorber is to the reference perfect absorber (square absorption band with absorption of 95% or more). The dash-dotted curve shows the absorption for a coefficient of variation of -10 nm, integral value 0.65, central frequency CFA(l) 1556 nm, absorption A=0,998, and minimum absorption band WMA=138 nm. The dotted curve shows the absorption with a coefficient of variation of +10 nm, an integral value of 1.12, a center frequency of 1619 nm for CFA(1), an absorption A=1, and a minimum absorption band WMA=139 nm.

[0088] As can be seen, the nanostructured IR absorber absorbs over 95% of the incident light in a bandwidth of + / - 25 nm centered at 1380 nm. This performance of the nanostructured IR absorber is maintained even when considering potential variations in the structure during manufacturing of + / - 10 nm.

[0089] As can be seen from Figure 12, designs according to embodiments place the nanostructure resonances close together to create a broad band of absorption centered around the wavelength of interest. In this way, pixel designs according to embodiments can reduce the reflected IR of a given band at the metallization.

[0090] FIG. 16 illustrates graphically the band of minimum absorption (WMA) discussed with respect to FIG. 15 above.

[0091] It should be noted that the above description is merely an example configuration: alternative configurations can be implemented using additional or other units, sensors, etc.

[0092] Also, it should be noted that the division of the system into units is for illustrative purposes only, and the disclosure is not limited to any particular division of functionality in any particular unit.

[0093] It should also be appreciated that the embodiments describe methods in exemplary sequences of method steps, however the specific sequence of method steps is provided for illustrative purposes only and should not be construed as binding.

[0094] All units and entities described herein and claimed in the appended claims may be implemented as integrated circuit logic, e.g. on a chip, in an FPGA, etc., unless otherwise stated, and the functions provided by such units and entities may be implemented by software, unless otherwise stated. To the extent that the embodiments of the present disclosure described above are implemented, at least in part, using software-controlled data processing apparatus, it will be understood that computer programs providing such software control, and transmission, storage or other media on which such computer programs are provided, are envisaged as aspects of the present disclosure.

[0095] It should be noted that the present technique can also be configured as follows. [1] A back-illuminated pixel including a photodiode (301) and an infrared absorber (301) having embedded nanostructures (402, 403), wherein the infrared absorber (301) having embedded nanostructures (401, 402) is configured to absorb light (305) passing through the photodiode (301). [2] The back-illuminated pixel according to [1], wherein the infrared absorber (301) has a multi-layer structure including a first layer (701) and a second layer (702) arranged below the first layer (701), and the nanostructures (401, 402) are embedded in the first layer (701) of the multi-layer structure. [3] A back-illuminated pixel as described in [2], wherein the embedded nanostructures (401, 402) combine with the first and second layers (701, 702) to form a metasurface having the function of absorbing light (305). [4] A back-illuminated pixel according to [2] or [3], wherein the first layer (701) is made of a material A, the second layer (702) is made of a material B different from material A, and the nanostructures (401, 402) inserted in the first layer (701) are made of the same material as the second layer (702). [5] A back-illuminated pixel as described in [4], wherein material A is a dielectric and material B is a metal. [6] [5] A back-illuminated pixel as described in [5], wherein material A is silicon dioxide and material B is aluminum. [7] A back-illuminated pixel as described in [1] to [6], wherein the embedded nanostructures (401, 402) are arranged as a nanostructure array (403) having a spatially repeated pattern. [8] The back-illuminated pixel according to [7], wherein the nanostructure array (403) is structured as a repeating cell (404). [9] [8] A back-illuminated pixel as described in [8], wherein the cell period (d) of the nanostructure array (403) is independent of the pixel pitch.

[10] The nanostructure array (403) comprises spatially repeated structures (401, 402) in the back-illuminated pixel of [8] or [9].

[11] The structures (401, 402) of the nanostructure array (403) are located at the boundaries of the cell (404), a back-illuminated pixel of

[10] .

[12] The back-illuminated pixel according to

[10] or

[11] , wherein the structures (401, 402) of the nanostructure array (403) change their orientation in each row of the pattern.

[13] A back-illuminated pixel according to any one of

[10] to

[12] , wherein the structures (401, 402) of the nanostructure array (403) include horizontally positioned structures (401) and vertically positioned structures (402).

[14] The back-illuminated pixel according to any one of claims

[10] to

[13] , wherein the structures (401, 402) of the nanostructure array (403) have an elliptical or quasi-circular shape.

[15]

[14] A back-illuminated pixel according to

[14] , wherein the elliptical or quasi-circular shape is defined by a small diameter (a) and a large diameter (b).

[16] A back-illuminated pixel as described in

[15] , in which the cell period (d) is in the range of 10% around 564 nm, the small diameter (a) is in the range of 10% around 182 nm, and the large diameter (b) is in the range of 10% around 214 nm.

[17] A back-illuminated pixel as described in

[15] , in which the cell period (d) is in the range of 10% around 750 nm, the small diameter (a) is in the range of 10% around 298 nm, and the large diameter (b) is in the range of 10% around 333 nm.

[18] A back-illuminated pixel as described in

[15] , in which the cell period (d) is in the range of 10% around 850 nm, the small diameter (a) is in the range of 10% around 350 nm, and the large diameter (b) is in the range of 10% around 390 nm.

[19] The first layer has a first thickness t 1 SiO2 The first sublayer has a thickness t d and a first sub-layer having a thickness t 2 SiO2 and the second layer includes a third sublayer having a thickness of t al

[18] . The back-illuminated pixel according to any one of [2] to

[18] , having a thickness of

[20] Thickness t 1 SiO2 is within 10% of the 50 nm range, and the thickness t al is within 10% of 60 nm, and the thickness t 2 SiO2is within 10% of the thickness t d is in the 10% range around 20 nm, for a back-illuminated pixel as described in

[19] . [twenty one] Thickness t 1 SiO2 is within 10% of the 38 nm range, and the thickness t al is within 10% of 60 nm, and the thickness t 2 SiO2 is within 10% of the 190 nm range, and the thickness t d is in the 10% range around 20 nm, for a back-illuminated pixel as described in

[19] . [twenty two] Thickness t 1 SiO2 is within 10% of the 45 nm range, and the thickness t al is within 10% of 60 nm, and the thickness t 2 SiO2 is within 10% of the 190 nm range, and the thickness t d is in the 10% range around 20 nm, for a back-illuminated pixel as described in

[19] . [twenty three] A back-illuminated pixel according to any one of [1] to

[22] , wherein an infrared absorber having nanostructures is located on a metallization layer (303), and an infrared absorber layer (701) having embedded nanostructures (402, 403) prevents light (305) from reaching the metallization layer (303). [twenty four]

[23] . The back-illuminated pixel according to any one of [1] to

[23] , wherein the infrared absorber (301) is configured to absorb light having a central wavelength of about 940 nm, 1380 nm, or 1550 nm. [twenty five] 2. The back-illuminated pixel of claim 1, wherein the back-illuminated pixel has a filled trench isolation (FTI) at a boundary with an adjacent pixel.

[26] The back-illuminated pixel according to any one of [1] to

[25] , wherein the back-illuminated pixel has deep trench isolation (DTI) at a boundary with an adjacent pixel.

[27] A sensor device comprising a photodiode array (1002) having a plurality of back-illuminated pixels according to any one of [1] to

[26] .

[28] The sensor device according to

[27] , wherein the photodiode array (1002) comprises an additional IR absorber (1001) arranged above the photodiode array.

[29] The sensor device of

[28] , wherein an additional IR absorber (1001) arranged above the photodiode array is configured to provide the functionality of an anti-flare shield and / or an on-pixel barrier (OPB) shield.

[30] A camera device comprising a sensor device according to any one of

[27] to

[29] .

Claims

1. 1. A back-illuminated pixel comprising: a photodiode and a nanostructured embedded infrared absorber, the nanostructured embedded infrared absorber configured to absorb light passing through the photodiode.

2. 2. The back-illuminated pixel of claim 1, wherein the infrared absorber has a multi-layer structure including a first layer and a second layer disposed below the first layer, and the nanostructures are embedded in the first layer of the multi-layer structure.

3. 3. The back-illuminated pixel of claim 2, wherein the embedded nanostructures combine with the first layer and the second layer to form a metasurface capable of absorbing light.

4. 3. The back-illuminated pixel of claim 2, wherein the first layer is made of a material A, the second layer is made of a material B different from material A, and the nanostructures inserted in the first layer are made of the same material as the second layer.

5. The back-illuminated pixel of claim 4 , wherein material A is a dielectric and material B is a metal.

6. The back-illuminated pixel of claim 5 , wherein material A is silicon dioxide and material B is aluminum.

7. 10. The back-illuminated pixel of claim 1, wherein the embedded nanostructures are arranged in a nanostructure array having a spatially repeated pattern.

8. The back-illuminated pixel of claim 7 , wherein the nanostructure array is structured as a repeating cell.

9. 10. The back-illuminated pixel of claim 8, wherein a cell period of the nanostructure array is independent of a pixel pitch.

10. The back-illuminated pixel of claim 8 , wherein the nanostructure array comprises spatially repeated structures.

11. The back-illuminated pixel of claim 10 , wherein the nanostructure array structures are located at boundaries of a cell.

12. The back-illuminated pixel of claim 10 , wherein the structures of the nanostructure array change orientation in each row of the pattern.

13. 11. The back-illuminated pixel of claim 10, wherein the nanostructure array features include horizontally positioned features and vertically positioned features.

14. The back-illuminated pixel of claim 10 , wherein the nanostructure array structures have an elliptical or quasi-circular shape.

15. The back-illuminated pixel of claim 14 , wherein the elliptical or quasi-circular shape is defined by a small diameter and a large diameter.

16. 16. The back-illuminated pixel of claim 15, wherein the cell period is in a range of 10% around 564 nm, the small diameter is in a range of 10% around 182 nm, and the large diameter is in a range of 10% around 214 nm.

17. 16. The back-illuminated pixel of claim 15, wherein the cell period is in a range of 10% around 750 nm, the small diameter is in a range of 10% around 298 nm, and the large diameter is in a range of 10% around 333 nm.

18. 16. The back-illuminated pixel of claim 15, wherein the cell period is in a range of 10% around 850 nm, the small diameter is in a range of 10% around 350 nm, and the large diameter is in a range of 10% around 390 nm.

19. The first layer has a first thickness t １ ＳｉＯ２ A first sub-layer having a thickness t ｄ and a second sub-layer having a first thickness t ２ ＳｉＯ２ and a third sub-layer having a thickness of t ａｌ The back-illuminated pixel of claim 2 having a thickness of

20. The thickness t １ ＳｉＯ２ is within 10% of the 50 nm range, and the thickness t ａｌ is within 10% of the 60 nm range, and the thickness t ２ ＳｉＯ２ is within 10% of the thickness t ｄ 20. The back-illuminated pixel of claim 19, wherein is in a 10% range around 20 nm.

21. The thickness t １ ＳｉＯ２ is within 10% of the thickness t ａｌ is within 10% of the 60 nm range, and the thickness t ２ ＳｉＯ２ is within 10% of the 190 nm range, and the thickness t ｄ 20. The back-illuminated pixel of claim 19, wherein is in a 10% range around 20 nm.

22. The thickness t １ ＳｉＯ２ is within 10% of the thickness t ａｌ is within 10% of the 60 nm range, and the thickness t ２ ＳｉＯ２ is within 10% of the 190 nm range, and the thickness t ｄ 20. The back-illuminated pixel of claim 19, wherein is in a 10% range around 20 nm.

23. 10. The back-illuminated pixel of claim 1 , wherein the infrared absorber having nanostructures is located above a metallization layer, and the infrared absorber layer with embedded nanostructures prevents light from reaching the metallization layer.

24. 10. The back-illuminated pixel of claim 1, wherein the infrared absorber is configured to absorb light having a central wavelength near 940 nm, or 1380 nm, or 1550 nm.

25. The back-illuminated pixel of claim 1 , wherein the back-illuminated pixel comprises filled trench isolation at a boundary with an adjacent pixel.

26. The back-illuminated pixel of claim 1 , wherein the back-illuminated pixel comprises deep trench isolation at a boundary with an adjacent pixel.

27. A sensor device comprising a photodiode array having a plurality of back-illuminated pixels according to claim 1.

28. 30. The sensor device of claim 27, wherein the photodiode array comprises an additional IR absorber disposed above the photodiode array.

29. 30. The sensor device of claim 28, wherein an additional IR absorber disposed above the photodiode array is configured to provide anti-flare shield and / or on-pixel barrier shield functionality.

30. A camera device comprising the sensor device of claim 27.

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