Optical detector unit and multispectral optical sensor, in particular for sectored viewing applications

Abstract

An optical detector unit (10) comprising an optical sensor unit (14) arranged on a substrate (12) to detect received photons, should allow for sectored viewing applications at a particular lean and simple setup at reduced manufacturing costs. This in accordance with the invention is achieved in that said optical sensor unit (14) comprises a number of detector arrays (24) each forming a respective detector spectral channel (26), wherein each detector array (24) comprises a number of sensor pixels (16) each generating a multispectral sensor signal as part of the respective detector channel (26), and an aperture element (30) is provided, with respect to said substrate (12), above said optical sensor unit (14), said aperture element (30) comprising a flat, laterally extending refractor element (32) defining a top surface (34) and a bottom surface (36), wherein said top and bottom surface (34, 36) are provided with a top aperture layer (38) and a bottom aperture layer (40), respectively, said top aperture layer (38) and said bottom aperture layer (40) are provided with a number of top apertures (42) and bottom apertures (44), respectively, said top apertures (42) and bottom apertures (44) being arranged pairwise, thereby forming a number of double apertures (46), and for each of said sensor pixels (16), a separate one of said double apertures (46) associated there-with is provided.

Description

[0001] Optical Detector Unit and Multispectral Optical Sensor , in particular for Sectored Viewing Applications

[0002] DESCRIPTION

[0003] Technical background of the invention

[0004] The invention relates to an optical or spectral detector unit . The invention more particularly relates to an optical detector unit comprising an optical sensor arranged on a substrate to detect received photons , said optical sensor comprising a number of sensor pixels each generating a multispectral sensor signal as part of one of a number of detector channels . The invention furthermore relates to a multispectral sensor comprising such an optical detector unit .

[0005] Background

[0006] Optical or multispectral sensors are increasingly being used in such diverse areas of technology as smart phones and mobile devices , smart homes and buildings , industrial automation, medical technology, connected vehicles , etc . At the same time sensor data becomes more complex and is expected to meet the requirements for high accuracy . Further, color and spectral light sensing on a chip-scale have various applications in color identi fication, data authentication, spectroscopy, and other industrial and consumer-level optical detection applications . In a number of important applications , in particular for camera applications , such sensors are used as ambient light sensors for so-called "auto white balance" functionality, in order to provide essential background information for appropriate correction functionalities and thereby in general improve imaging quality .

[0007] Common multispectral sensors are often based on an array of pixels and on-pixel filters for each pixel . For spectroscopic applications the filters can be chosen to have linear inde- pendent filter characteristics . In order to accomplish an accurate spectral measurement of a given source , incoming radiation should be known in order to compensate for di f ferent response of individual pixels . This way an amplitude of a spectral signal of a pixel can be used to calculate a spectral reconstruction of a light source under study .

[0008] However, a homogenous distribution of incoming radiation on the pixel array is an ideal condition . In real systems , in contrast , variations of the actual irradiation detected at the sensor ' s level may vary between di f ferent channels , due to geometry ef fects limiting the individual field of views ( FOV) , dominant angle of incidence (AOI ) of incoming irradiation, etc . Geometry ef fects in such systems may be caused by misalignments of individual components due to manufacturing tolerances etc . In particular for uses in ambient light sensor devices , however, homogeneity of incoming light distribution at detector level may be of special signi ficance . In order to provide highly reliable homogenous distribution, di ffusors may be used in a position before incoming radiation reaches the pixels in order to mix the incoming light as well as possible and to pass on the light to the sensor array in a homogenous , ideally in a Lambertian, manner . Further, the spectral sensitivity of an interference filter-based multi- spectral sensor depends strongly on the angular distribution of light hitting the filter on the detector array .

[0009] Further, in many existing sensor devices for a mean limit of the field of view (" FOV" ) a lid aperture is used in combination with a di f fuser on top or, with respect of the direction of incoming light , in front of the aperture in order to collect and mix incoming light from a rather wide incident angle (up to 180 ° ) . The position of the lid with respect to the sensor array underneath, however, can vary largely because of tolerances and lack of precision in the packaging during the assembly process . Such variation in relative position may generate variations in amplitude and spectra shape of sensitivity, because of variations in angular power distribution . Depending on the array position, each channel will be af fect ed in a di f ferent way . Variations in angular distribution will generate variations in spectral sensitivity .

[0010] Depending on the performance of an associated di f fuser, the system accuracy may also depend on the position of a dominant radiation spot . A wide di f fuser obj ect will scatter the light more homogeneous to the inside into the detector array than a dominant and small point . Typically, each di f fuser with a common transmittance ratio also has an ideal Lambertian spread and will also vary the power distribution depending on the position ( tilt vs . detector ) and spectra sensitivity .

[0011] The knowledge about the setup depending on spectra sensitivity is important to generate a useful trans fer matrix for spectral reconstruction . However, especially for colored scenes , the typical white balancing by the "gray world theory" or the "brightest pixel theory" ( assuming the dominant contribution from a dominant radiation spot ) are restricted in balancing performance , and detailed color and spectral information about the ambient light is expected to improve the performance without color shi ft .

[0012] Further, especially in smart phone applications , camera systems with increasing performance may be provided . Improved cameras of this type may allow for optimi zed evaluation of detected color and spectral information in various sectors of the scene , such as center of the selected scene , borders of the scene , areas outside of the selected scene . It therefore may be highly desirable to provide improved ambient light sensors that are able to match increased camera performance by also taking into account the speci fics of the various scenarios or scenes supported by the camera for the respective white balancing .

[0013] For this purpose , ambient light sensors suitable for so- called sectored viewing with detectors allowing for a sectored view to a target scene may be provided . In particular, designs for the sectored viewing of color and / or spectral sensors based upon micro-lens array ("MLA" ) packages have been suggested . In such designs , for each spectral channel a single , associated optical path is provided for generating a monochromatic image on a detector array . Regarding the tolerances in MLA production or deposition processes , however, as well as the relatively high tolerances in packaging processes , the viewing angle of each spectral channel can tilt in a di f ferent direction, requiring further compensation . This results in signi ficant ef forts in final testing and custom operating of such devices . Further, because of the relatively low pixel counts and the ef fects of dominant structure movements in such devices , an optical system may be needed to blur and smoothen the scenery image and the detection .

[0014] Summary

[0015] The obj ect of the invention is therefore to provide an improved optical detector unit of the type identi fied above , comprising an optical sensor with suitable for sectored viewing, that helps overcome the deficiencies identi fied above , in particular in a particular lean and simple setup in order to reduce manufacturing costs . Further, an improved multi- spectral sensor should be provided .

[0016] With respect to the optical detector unit , this obj ect is achieved in that :

[0017] - the optical sensor unit comprises a number detector arrays each forming a respective detector spectral channel , wherein

[0018] - each detector array comprises a number of sensor pixels each generating a multispectral sensor signal as part of the respective detector channel , and

[0019] - an aperture element provided, with respect to a substrate , above said optical sensor unit , said aperture element comprising a flat , laterally extending refractor element defining a top surface and a bottom surface , wherein :

[0020] - said top and bottom surface of said aperture element are provided with a top aperture layer and a bottom aperture layer, respectively,

[0021] - said top aperture layer and said bottom aperture layer are provided with a number of top apertures and bottom apertures , respectively, said top apertures and bottom aper- tures being arranged pairwise , thereby forming a number of double apertures ,

[0022] - for each of said detector channels , a separate one of said double apertures associated therewith is provided, and

[0023] - for all of said sensor pixels of one or each of the detector arrays , a j oint di f fuser element is provided .

[0024] Preferred embodiments are subj ect of the dependent claims .

[0025] The invention is based on the consideration that , in comparison to MLA based design concepts for a sectored view sensor, a signi ficant part of the potential deficiencies mentioned above are considered to be consequences of the relatively complex design and manufacturing process for the micro-lens arrays . In particular, a main source of errors and inaccuracies in the present consideration is associated with the relative adj ustment of the individual components in relation to each other, particularly in view of the inevitable manufacturing tolerances . Consequently, in such conventional systems di f ferences and variations between individual pixel or channels with respect to detection of incoming radiation will be caused by di f ferences of their individual positioning relative to the associated micro lens system . In order to overcome this potential source of inhomogeneity between individual channels , the present invention suggests to provide a separate , individual aperture to each channel in order to facilitate the sectored view goal , and the individual MLAs should be replaced by the double aperture systems . The optical and transmission characteristics of each channel may then be provided with the necessary accuracy in the design and positioning of each individual aperture , and homogeneity and comparability between di f ferent channels may be ensured by proper, highly accurate manufacturing of the aperture system .

[0026] In particular, in one aspect , the present invention suggests to generate the sectored view by a pixel wise double aperture array . The viewing angle , the field of view (" FOV" ) and the smoothing in this design may be defined by the diameters , distance , diameter ration and of f axis shi ft of the individual double aperture .

[0027] In one aspect of the invention, this "one separate aperture per pixel" approach may be achieved by providing a common, j oint aperture element for the ensemble of channels , in which a central refractory element of planar shape , on both its planar sides , is provided with an aperture layer each providing a number of openings or apertures . The layers and their openings or apertures then may be arranged on the two planar sides of the refractory element such that in a pairwise structure each aperture in the first layer has a counterpart aperture in the second layer positioned "on top" or in the same lateral space as its counterpart , thereby forming double aperture structures that may be individually associated with individual sensor pixels . In principle , this "one aperture per pixel"-concept might be achieved by j ust one aperture layer, which is necessary to properly define the FOV of the sensor underneath . Preferably, the upper or top aperture layer is provided in this way . The additional , lower aperture layer preferably is also provided in order to properly define the optical geometries .

[0028] In one aspect of the invention, for each of the sensor pixels , the double aperture associated therewith may define a "main line of view" of the respective sensor pixel . This main line of view identi fies the main direction from which radiation is received by the respective pixel , and the individual FOV of the respective pixel is centred around this main line of view and limited by the geometrical conditions of the individual double aperture associated with the respective pixel . In consequence , by definition of such "main line of view" for each pixel , the double aperture defines the field of view ( FOV) and the viewing orientation ( sector ) of the respective pixel . Thus , in an aspect of the invention by proper choice and selection of the various geometry parameters of the double aperture , such as shape and si ze of the two apertures , their respective lateral positions on the j oint aperture element relative to each other, the thickness of the aperture element , both the main line of view and the FOV of each individual pixel may be designed at high precision . In consequence , in an embodiment of the invention, the detector may easily be designed for sectored view applications by providing adequate requirements for the parameters of the individual pixels . In a preferred embodiment , for each of said detector channels , at least two of their sensor pixels have main lines of view di f ferent from each other, thereby enabling sectored view designs in a very easy and versatile manner .

[0029] In a preferred embodiment , the refractor unit is a glass element , in particular a glass wafer or a glass substrate or spacer . In this aspect of the invention, a glass-based aperture element is provided . The glass element is provided with a channel-wise aperture structure and optical configuration, positioned on top of the detector array and defining the structure of detector arrangement . The aperture unit in this aspect of the invention consists of the glass element having a first or top aperture layer and a second or bottom aperture layer . For the layers , in an aspect of the invention a material with high absorption and minimum transmission is selected, such as "black Chromium" . Alternatively, a properly designed stack of interference filters comprising further metal layers may also be provided .

[0030] This aperture unit may be provided on a TSV chip with diodes . The FOV for each channel in this setup is defined by the diameter of the apertures on first and second aperture layer on and underneath the glass element , the distance of the glass element from the substrate , the thickness of the glass , the refractive index of the glass , and the relative lateral positions of the two apertures relative to each other . Accurate processes of aperture mask and waver scale mounting in this preferred embodiment guarantee the desired angular power distribution for all spectral channel since these parameters due to high production and manufacturing standards may be provided identically for all channels . Depending on the individual application and use case of the detector unit , in a preferred embodiment of the invention, for each of the detector arrays , a di f fuser element may be provided . In other words , even though a separate double aperture may be provided for each individual pixel , nevertheless a j oint di f fuser may be provided as a common di f fuser for all pixels forming the respective array or channel . Preferably, this di f fuser element may positioned between the substrate and the aperture element .

[0031] The aperture element , depending on the individual use case and potential other parameters or requirements , may be positioned distanced from the substrate carrying the sensor unit , thereby leaving some type of gap between the surface of the substrate and the bottom aperture layer . The di f fuser element or layer may be arranged directly on top of the detector element and / or directly in contact with the second or bottom aperture layer . I f a gap is to be provided, this gap can be positioned between di f fuser and substrate or between di f fuser and bottom aperture layer .

[0032] Each pixel may comprise a photodiode as the signal-generating unit . According to a preferred aspect of the invention, the detector channels each comprise at least one of said pixels and an optical filter associated therewith . As in comparable sensor designs , in such a design the filter determines the transmission characteristic of the respective sensor pixel . In an embodiment of the invention, such ensemble of pixel or photodiode with associated optical filter may be provided in a stacked or package type of design in close proximity to each other . In particular, in a preferred embodiment , for each of said detector arrays , an interference filter suitable for the detector spectral channel formed by the respective detector array is provided . In yet another aspect of the present invention which is considered independently inventive , a j oint interference filter may be provided for all pixels of the same detector array or the same detector channel . In an aspect of the invention, the detector unit is manufactures in an integrated chip design, preferably combining the concept identi fied above with modern wafer level chip scale packaging ("WLCSP" ) technologies in order to obtain a reliable , yet cost-ef fective compact and miniaturi zed sensor design using only few components . In an aspect of the invention, the detector unit is designed in WLCP technology .

[0033] In a preferred embodiment , the pixels each have a di f ferent transmission characteristics , preferably are linearly independent .

[0034] Further, in yet another aspect of the invention and in view of the intended application or use of detector unit in an ambient light sensor (ALS ) , preferably about 5 to 12 channels with di f ferent transmission characteristics , in particular peak spectral sensitivity, are provided . In view of this preferred number range for the channels , and taking into account the desired at least approximate reconstruction of the detected spectrum in the visible range , in preferred embodiment the spectral sensitivity of some or each of the channels is of cosine shape , with the Full Width Hal f Maximum ( FWHM) width being approximately equal to the separation between adj acent peaks . In yet another embodiment , the spectral sensitivity of one or each channel may be of Gaussian shape .

[0035] With respect to the multispectral sensor, the obj ect mentioned above is achieved in that the multispectral sensor comprises an optical detector unit of the type identi fied above . Further, in a preferred embodiment and in accordance with yet another aspect of the invention, the multispectral sensor is intended for use as an ambient light sensor, in particular for use in camera systems , and preferably in applications for sectored viewing of the ambient light sensor .

[0036] The maj or advantages achieved by the invention may be seen in that due to the basic concept of the invention of providing separated optical channels in which the respective pixel of each channel is associated with an individual aperture system allows for the channels to have individually designed optical and geometrical performance at low tolerances . Therefore , the detector unit , at high accuracy and reliability, even for sectored view applications may be designed without the necessity to use special optical or MLA elements , and therefore is particularly suitable for advanced production technologies and miniaturi zed designs . In consequence , enhanced optical and spectral performance may be achieved at lowered costs and lowered number of components .

[0037] In other words , according to the concept of the invention, each pixel is provided with its own, associated optical aperture . It further is geometrically separated from neighbouring pixels , thereby preventing or at least minimi zing cross talk between channels or even pixels . The pixel-wise optical separation defines similar and comparable optical performance ( FOV, synchronic alignment , power distribution on filter, ... ) for all the colour or spectral channels without the necessity for additional optical components . In particular, sectored view may be generated by a pixelwise double aperture array wherein a number of pixels forming a subarray or the entire ensemble of pixels define the respective detector spectral channel . The viewing angle , the field of view (" FOV" ) and the smoothing in this design may be de- fined by the diameters , distance , diameter ration and of f axis shi ft of the individual double aperture . The spectral channels are a setup of on chip di f fuser, that generates an AOI independent Lambertian mix of light , and for those Lambertian characteristic spectral designed filters on chip .

[0038] In particular, for enabling sectored view applications , instead of using a comparatively rather expensive optical structure ( such as MLA) and multi-pixel designs for supporting interpolation approaches to compensate alignment issues , a comparatively simple double aperture is used to define the individual sectors of viewing . The main viewing angle for each channel or pixel may be designed flexibly by arranging several shi fts of upper and lower apertures . Overlap of filter and detector may be defined by alignment accuracy of the aperture relative to the detector, the main spread of the di f fuser ( > thickness of di f fuser ) , the minimum gap of aperture defined by glass thickness and refractive index => max AOI in glass 41 ° . Further, a comparatively ef ficient design may be achieved since the reduced power ef ficiency due to the potentially small aperture si zes is compensated by only needing one compact detector per segment rather than in the MLA approach in which 3x3 pixels are needed for overcompensation .

[0039] Yet further, due to the channel-wise optical configuration of the individual pixels of the various spectral channels as provided in an aspect of the present invention, preferably in combination with the high accuracy of available modern process technology, allows for low tolerances and increased optical and spectral performance . The arrangement in yet another consequence gives more freedom in distribution of optical channels over the chip area, since no common element such as a j oint di f fuser needs to be provided for all channels . Therefore , the individual channels may be spaced relatively wide apart from each other on the chip, thereby providing gaps between adj acent channels that might be filled in smart arrangements with circuit parts or other electronic components on the chip .

[0040] In summary, the main advantages of the present invention may be seen in a relatively simple and cheap principal solution, the possible use of existing technologies , no need for additional optical elements , reduced pixel count ( resulting in fast readout and lower chip costs ) , smoothing done by aperture structure , no need for geometrical compensation because of high accuracy (<lpm) in waver scale aperture processing, independence from package tolerances , and reduced ef fort in final testings and custom operations .

[0041] Brief Description of the Preferred Embodiments

[0042] Preferred embodiments and aspects of the invention are described further in connection with a drawing . In this drawing, FIG . 1 shows a smartphone in backside view;

[0043] FIG . 2 shows a camera system, in particular for use in the smartphone of FIG . 1 ;

[0044] FIG . 3 shows a detector array of an optical detector unit of the camera system of FIG . 2 ;

[0045] FIG . 4 shows an optical detector unit of the camera system of FIG . 2 in cross section;

[0046] FIG . 5-7 each show another alternative embodiment of an optical detector unit of the camera system of FIG . 2 in cross section .

[0047] Identical parts are labelled by the same reference numerals .

[0048] Detailed Description of the Preferred Embodiments

[0049] FIG . 1 shows a smartphone 1 in backside view . The smartphone 1 is equipped with a camera system 2 , which, as its maj or components , comprises the actual camera 4 , also referred to as the "camera detection system" 4 , and a multispectral sensor 6 , serving as an ambient light sensor 6 , associated therewith . The camera sensor system 4 , the details of which are of lesser signi ficance for the invention disclosed here , and the ambient light sensor 6 are mounted at the back of a common cover glass 8 , which may be the cover glass 8 of the smartphone 1 as such . The ambient light sensor 6 is used mainly for so-called "auto white balance" functionality in the camera system 2 , in order to provide essential background information for appropriate correction functionalities and thereby in general improve imaging quality of the camera system 2 .

[0050] FIG . 2 shows an example of the camera system 2 in cross section that in the embodiment shown is integrated into a mobile device such as the smartphone 1 . It is noted, however, that the concept presented below may very well be used in other systems or devices , such as wearables . The ambient light sensor 6 comprises an optical detector unit 10 in the form and design of an optical sensor chip . It is noted that the concept proposed herein can be applied for various types of optical sensor chips and optical devices and that the present invention relates to the design of the optical detector unit 10 alone and therefore , within the scope of the present invention, may very well be used in an optical detector unit 10 in other applications .

[0051] The optical detector unit 10 comprises a housing 11 in which a carrier or substrate 12 is positioned . The substrate 12 provides mechanical support and electrical connectivity to electronic components which are integrated into the optical detector unit 10 . In the embodiment shown, the substrate 12 together with the electronic components integrated therein is designed in the so-called wafer level chip scale packaging ("WLCSP" ) technology .

[0052] As part of the optical detector unit 10 , an optical sensor unit 14 is arranged on the carrier 12 to detect received photons . In this particular embodiment , the optical sensor 14 is integrated into a single semiconductor sensor die 15 together with other electronics . The optical sensor 14 comprises a number of individual optical detector elements or pixels 16 each generating a multispectral sensor signal . The pixels 16 may be implemented as photodiodes , for example . The pixels 16 are disposed on the substrate in some predetermined pattern, in particular in an array .

[0053] A control unit and a measurement unit (not shown) are integrated into the semiconductor sensor die 15 alongside with the optical sensor 14 . The measurement unit can be considered a control unit for the optical sensor unit 2 . For example , it may provide sensor signals which are generated by the optical sensor 14 . The control unit and the measurement unit may be implemented as control logic, state machines , microprocessor and the like . They may also comprise additional components such as analog-to-digital converters , time-to-digital converters , ampli fiers which too may be located in the semiconductor sensor die 15 . The semiconductor die 15 may have a printed circuit board PCB providing electrical communication to the individual components of the multispectral sensor . In operation, incoming radiation can be detected by means of the optical sensor 14 . Each sensor pixel 16 in reaction generates a multispectral sensor signal , respectively . The measurement unit therefore in total provides a set of multispectral sensor signals .

[0054] In the embodiment shown in FIG . 2 , the housing 11 may be attached to the cover glass 8 indirectly, with a di f fuser element 17 and / or a block filter or IR cut filter 18 positioned therebetween . Also shown in FIG . 2 are cones 20 , 22 , indicating the fields of view ( FOV) of the camera 4 and the ambient light sensor 6 , respectively . The field of view of an optical device includes all points in space from where , at least theoretically, light radiated from an external radiation or light source may traverse towards the device , e . g . for a fixed detector position and orientation . As can be seen from FIG . 2 , the cone 22 representing the FOV of the ambient light sensor 6 is signi ficantly larger than the cone 20 representing the FOV of the actual camera 4 , due to the general desire for ambient light sensors to have a huge field of view and, if possible , to detect light from the complete solid angle .

[0055] In modern cameras , however, various options may be of fered to the user that include focussing on certain scenes , taking into account areas neighbouring the focus area, etc . For such systems , the conventional design approach for ambient light sensing, i . e . the typical white balancing by the "gray world theory" or the "brightest pixel theory" are restricted in balancing performance and thus may be not suf ficient for the requirements of enhanced camera performance . In order to overcome this and to provide an ambient light sensor 6 enabled to properly support the camera 4 and produce enhanced and improved white balancing, the ambient light sensor 6 is designed to give sectored color and spectral information of the scene and parts around ( centre of the scene , border of the scene and outside areas of the scene ) . In other words , the ambient light sensor 6 is designed for so-called sectored viewing applications . The sectored information of ef fective ambient light may then be used to produce a gradient white balancing of the image and to adj ust to di f ferent ambient light conditions in one scene . The design for sectored viewing in FIG . 2 is represented by dashed lines 23 , dividing the core 22 representing the FOV of the ambient light sensor 6 into a number ( in the embodiment shown three ) of sectors of the FOV of the ambient light sensor 6 .

[0056] In order to achieve this enablement for sectored view, in accordance with one aspect of the present invention, the pixels 16 of the ambient light sensor 6 are grouped into subarrays , in particular into monochromatic detector arrays 24 , each of which forming a respective detector spectral channel 26 with its own filter and optic, thereby allowing for an on chip integration and wafer scaled package . The geometrical design of the detector arrays 24 and their respective optical stack define the sectoring of the sensor ' s fields of view .

[0057] This arrangement of the pixels 16 into subgroups forming individual monochromatic detector arrays is schematically shown in FIG . 3 which presents a top view onto the arrangement of the pixels 16 on the sensor die 15 . In the embodiment shown, a symmetric design is chosen for the monochromatic arrays 24 and their optical stacks such that each pixel 16 within the respective array 24 is associated with the same sector of a scene , which is necessary for colorimetric analysis . In consequence of this arrangement of the pixels 16 , in an aspect of the present invention the full field of view ( FOV) of the ambient light sensor 6 is split into FOV segments wherein the detector arrays 24 are detecting the average light of each segment . This setup of strictly separating into segments is not sensitive to position-dependent structures of incoming radiation, such as bright dot light sources . As long as such structure is part of the segment it is also part of the averaging of the segment . In the embodiment shown in FIG . 3 , twelve detector spectral channels 26 , each formed by an array 24 of pixels 16 , are provided .

[0058] A section of the optical detector unit 10 of the ambient sensor 6 , comprising only two of the detector arrays 24 , is shown in enlarged cross-sectional view in FIG . 4 . As shown in FIG . 4 , as a further part of each respective detector spectral channel 26 of the optical detector unit 10 , an associated optical filter element , in the preferred embodiment shown an interference filter element 28 common to all pixels 16 of the respective channel 26 , is provided . In the embodiment shown, the optical filter element 28 is positioned directly on top of the associated pixels 16 . The filter element 28 is designed such that the pixels 16 belonging to the same spectral channel 28 have the same transmission characteristic whereas di f ferent spectral channels 26 have di f ferent transmission characteristics ; preferably, their transmission characteristics may be linearly independent . In various embodiments , the optical filter elements 28 may be interference filters such as an optical cut-of f filter, bandpass , long or short pass filter, dielectric filters , Fabry-Perot filters and / or polymer filters .

[0059] In order to enable the detector unit of the ambient light sensor 6 for the intended sectored viewing capabilities , and to provide a multispectral optical detector unit 10 with improved performance , in accordance with an aspect of the present invention, the detector unit 10 in the embodiment shown is designed in a "one aperture per pixel 16" layout .

[0060] In view of the design goal of sectored viewing capability, the optical detector unit 10 comprises an aperture element 30 provided, with respect to the substrate 12 , above the optical sensor unit 14 . The aperture element 30 comprises a flat , laterally extending refractor element 32 which in the embodiment shown is a glass element , but may be chosen from any other material considered suitable in view of aspects like proper refraction index, proper transmission characteristics , availability, costs , etc . Due to its basic shape of a flat , laterally extending body, the refractor element 32 defines a top surface 34 , in the mounted state shown in FIG . 4 facing away from the substrate 12 carrying the sensor unit 14 , and a bottom surface 36 , in the mounted state shown in FIG . 4 facing towards the substrate 12 carrying the sensor unit 14 .

[0061] The top surface 34 , and equivalently the bottom surface 36 , are provided with a top aperture layer 38 and a bottom aperture layer 40 , respectively . The aperture layers 38 , 40 in the embodiment shown are made of a material with high absorption and minimum transmission, such as "black Chromium" . Alternatively, a properly designed stack of interference filters comprising further metal layers may also be provided . The top aperture layer 38 is provided with a number of openings through which radiation can pass , thereby each providing a top aperture 42 . Correspondingly, the bottom aperture layer 40 is provided with a number of bottom apertures 44 . As shown in FIG . 4 , in their lateral positions in the top / bottom surface 34 , 36 , respectively, the top apertures 42 and bottom apertures 44 are arranged pairwise in the sense that each top aperture 42 is positioned right on top or in the direct proximity of a corresponding bottom aperture 44 , thereby forming a number of double apertures 46 . The deposition of the aperture layers 38 , 40 onto the glass substrate providing the refraction element 32 may be easily ef fected by modern standard deposition technologies with high accuracy, as well as the production of the aperture patterns both in the top aperture layer 38 and the bottom aperture layer 40 may be ef fected with high precision with lithographic methods .

[0062] As can be seen in FIG . 4 , for each of the pixels 16 , a separate one of the double apertures 46 associated therewith is provided . Thus , the embodiment shown provides a detector unit 10 designed with a pixel-wise aperture system and optical configuration, using a glass-based refractor element 32 on top of a detector array, defining the structure of the detector arrangement . The aperture element 30 basically consists of a glass with a first ( top ) aperture layer 38 and and a second (bottom) aperture layer 40 . The detector unit 10 com- prises this aperture element 30 in addition to a TSV chip with photodiodes providing the sensor pixels 16 . Due to the individual association of one double aperture 46 with each of the pixels 16 , respectively, the respective , associated double aperture for its pixel 16 defines its key properties such as a main line of view, as represented by arrow 48 , and FOV .

[0063] Both the main line of view and the FOV for each pixel 16 are defined by the diameter of the associated apertures 42 , 44 on first and second aperture layer 38 , 40 on glass 32 , the thickness of the glass 32 , the refractive index of the glass 32 , and the lateral displacement of the respective top aperture 42 with respect to its corresponding bottom aperture 44 . The FOV in FIG . 4 is indicated by arrows 50 indicating the limiting rays of the respective FOV of the individual pixels 16 ; as shown in FIG . 4 , due to the refractive ef fects of refractor element 32 , the direction of propagation of these rays changes at the top surface 34 of the refractor element 32 . The main line of view of each pixel 16 in this context should be understood as a "centre line" of the FOV of the respective pixels , and thus identi fies the main direction from which radiation is received by the respective pixel 16 . Therefore , the individual FOV of the respective pixel 16 is understood to be centred around this main line of view, and both the main line of view as well as the FOV of each pixel 16 are limited by the geometrical conditions of the individual double aperture 46 associated with the respective pixel 16 .

[0064] As can be seen from FIG . 4 , in order to achieve the capability of sectored viewing, di f ferent pixels 16 of one and the same channel 26 , by appropriate choice and design of their associated double apertures 46 , in one embodiment of the invention are designed for di f ferent main lines of view . In consequence , in any of the arrays 24 forming the respective channels 26 , by variation of the geometry parameters of the associated double apertures 46 , various pixels 16 may be designed for di f ferent main lines of view, thereby allowing for sectored viewing by assigning individual pixels 16 to individual sectors of the respective FOV.

[0065] Accurate processes of aperture mask and wafer scale mounting, as widely available, guarantee the precise realization of the desired properties, in particular the differentiation of different main lines of view for different pixels 16 and thereby their association to different sectors of the overall FOV.

[0066] Depending on the refractive index for instance inside of the glass 32, the AOI will be always less than 41°. In correlation to the glass thickness, this defines the minimum absorbing layer width between the channels 24.

[0067] The embodiment shown in FIG. 4 shows a layout of 4x4 pixels 16 per channel 26. Of course, this allocation of individual pixels 16 is scalable, and other configurations such as 2x2 pixels 16 per channel 26 or 3x3 pixels 16 per channel 26 may be chosen.

[0068] As a further component, and according to one aspect of the invention, a diffuser element 52 may be provided for the pixels 16 of a respective channel 26. In the embodiment shown in FIG. 4, a single diffuser element 52 is provided for the entire ensemble of pixels 16 of the respective channel 26. The diffuser element 52 is provided in the form of a diffuser film positioned directly on top of the respective interference filter elements 28. In this embodiment, the aperture element 30 with its bottom aperture layer 40 may rest directly on the diffuser element 52, thereby providing a particularly compact and robust overall setup. In this configuration, the aperture element 30 in the way of an additional functionality also serves as protection and cover for the sensor unit 14 and all potential additional electronics positioned underneath. Further, in comparison to conventional sensor systems, in this way the aperture element 30 may be considered to functionally replace the regular cover for the sensor unit 14, which typically is designed as a mould or an overmould. Beyond increased mechanical strength and durability provided by the aperture element 30 in this function, in comparison with the typical overmold the aperture element 30 due to the basic material of glass tends to signi ficantly less aging properties , and also lessened temperature dependence .

[0069] In another embodiment , however, as shown in FIG . 5 , the di ffuser element 52 may be attached to the bottom aperture layer 40 while leaving a gap 54 with respect to the substrate 12 , in particular to the interference filter elements 28 positioned on top of the sensor unit 14 . This additional air gap 54 between di f fuser 52 and filter elements 28 may be beneficial because of reduced angular distribution of incoming radiation on the filter element 28 . In yet another embodiment , as shown in FIG . 6 , the di f fuser element 52 may instead be attached to the substrate 12 , in particular to the interference filter elements 28 positioned on top of the sensor unit 14 , thereby leaving a gap 54 to the bottom aperture layer 40 .

[0070] In yet another embodiment , as shown in FIG . 7 in cross section, additional one or multiple aperture levels can be added on top of the aperture element 30 , in order to even further reduce cross talk, minimi ze the gap between channels , and / or enhance precision of defining individual sectors of viewing to respective pixels 16 . In such embodiments , three or more individual apertures are associated with an individual pixel 16 , and accordingly the "double aperture 46" of the previous examples in this embodiment may be referred to as an "multi aperture system 46" instead . In particular, preferred design parameters in accordance with one aspect of the invention, for glass substrate 12 and thin glass stacking, may be a thick first wafer ( 300- 900pm) for stability with upper aperture element 30 , thin glasses ( 30- l O Opm) for bonding and aperture underneath, and multi layer apertures to prevent cross talk and smaller pixel pitch .

[0071] The embodiments of the optical sensor device 2 discussed herein have been disclosed for the purpose of familiari zing the reader with novel aspects of the idea . Although preferred embodiments have been shown and described, many changes , mod- ifications , equivalents and substitutions of the disclosed concepts may be made by one having skill in the art without unnecessarily departing from the scope of the claims .

[0072] In particular, the disclosure is not limited to the disclosed embodiments , and gives examples of as many alternatives as possible for the features included in the embodiments discussed . However, it is intended that any modi fications , equivalents and substitutions of the disclosed concepts be included within the scope of the claims which are appended hereto .

[0073] Features recited in separate dependent claims may be advantageously combined . Moreover, reference signs used in the claims are not limited to be construed as limiting the scope of the claims .

[0074] Furthermore , as used herein, the term " comprising" does not exclude other elements . In addition, as used herein, the article " a" is intended to include one or more than one component or element , and is not limited to be construed as meaning only one .

[0075] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a speci fic order . Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise speci fically stated in the claims or descriptions that the steps are to be limited to a speci fic order, it is in no way intended that any particular order be inferred . LIST OF REFERENCE NUMERALS smartphone camera system camera detection system ambient light sensor cover glass optical detector unit housing substrate sensor unit sensor die pixel di f fuser element cut filter , 22 cone dashed lines detector array channel interference filter element aperture element refractor element top surface bottom surface top aperture layer bottom aperture layer top aperture bottom aperture double aperture , 50 arrow di f fuser element gap

Claims

CLAIMS1. An optical detector unit (10) comprising:- an optical sensor unit (14) arranged on a substrate(12) to detect received photons, said optical sensor unit (14) comprising a number of detector arrays (24) each forming a respective detector spectral channel (26) , wherein- each detector array (24) comprises a number of sensor pixels (16) each generating a multispectral sensor signal as part of the respective detector channel (26) , and- an aperture element (30) provided, with respect to said substrate (12) , above said optical sensor unit (14) , said aperture element (30) comprising a flat, laterally extending refractor element (32) defining a top surface (34) and a bottom surface (36) , wherein:- said top and bottom surface (34, 36) are provided with a top aperture layer (38) and a bottom aperture layer (40) , respectively,- said top aperture layer (38) and said bottom aperture layer (40) are provided with a number of top apertures (42) and bottom apertures (44) , respectively, said top apertures (42) and bottom apertures (44) being arranged pairwise, thereby forming a number of double apertures (46) ,- for each of said sensor pixels (16) , a separate one of said double apertures (46) associated therewith is provided, and- for all of said sensor pixels (16) of one or each of the detector arrays (24) , a joint diffuser element (52) is provided.

2. The optical detector unit (10) of claim 1, in which for each of said sensor pixels (16) , said double aperture (46) associated therewith defines a main line of view of the respective sensor pixel (16) .

3. The optical detector unit (10) of claim 2, in which for each of said detector channels (26) , at least two of their sensor pixels (16) have main lines of view different from each other.

4. The optical detector unit (10) of any one of claims 1 to3, in which said diffuser element (52) is positioned between said substrate (12) and said aperture element (30) .

5. The optical detector unit (10) of any one of claims 1 to4, in which the channels (26) each have a different spectral transmission characteristic.

6. The optical detector unit (10) of claim 5, wherein the different transmission characteristics of the channels (26) are linearly independent.

7. The optical detector unit (10) of any one of claims 1 to6, in which for each of said detector arrays (24) , an interference filter element (28) suitable for the detector spectral channel (26) formed by the respective detector array (24) is provided.

8. The optical detector unit (10) of any one of claims 1 to7, in which said refractor element (32) is a glass element .

9. A multispectral sensor, comprising an optical detector unit (10) of any one of claims 1 to 8.

10. The multispectral sensor of claim 9, which is designed as an Ambient Light Sensor (6) .

11. Camera system (2) comprising an ambient light sensor (6) having an optical detector unit (10) of any one of claims

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