Optical detector unit and multispectral optical sensor

Abstract

An optical detector unit (10, 10´, 10´´, 10´´´, 10´´´´) comprising an optical sensor unit (16) arranged on a substrate (12) to detect received photons, said optical sensor unit (16) comprising a number of sensor pixels (20) each generating a multispectral sensor signal as part of one of a number of detector channels (24), should allow for a particular lean and simple setup at reduced manufacturing costs. This in accordance with the invention is achieved in that an aperture element (30) is provided, with respect to said substrate (12), above said optical sensor unit (16), 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) such that in each double aperture (46) the top aperture (42) is arranged on top of its corresponding bottom aperture (44), and for each of said detector channels (24), a separate one of said double apertures (46) associated therewith is provided.

Description

[0001] Optical Detector Unit and Multispectral Optical Sensor

[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] 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 .

[0006] 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 independent filter characteristics . In order to accomplish an ac- curate spectral measurement of a given source , incoming radi- ation 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 .

[0007] 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 .

[0008] 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 different way. Variations in angular distribution will generate variations in spectra sensitivity.

[0009] Depending on the performance of an associated diffuser, the system accuracy may also depend on the position of a dominant radiation spot. A wide diffuser object will scatter the light more homogeneous to the inside into the detector array than a dominant and small point. Typically, each diffuser 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. The knowledge about the setup depending on spectra sensitivity is important to generate a useful transfer matrix for spectral reconstruction.

[0010] In order to compensate for these aspects different measurement systems have been proposed. These systems are based on robust optical construction or strictly defined measurement geometries, e.g. measurements under defined angles such as 45° / 0° or 22,5° / 22,5°, or using an integrating sphere. Such systems are typical for color measurement with strictly fading out of glossy and constant measurement distances. For compensation of non-homogenous radiance distribution by optics, mixing using diffusers and optical lenses is one possibility. However, the field of view, FOV, and size ratio are often not practical. Other solutions employ image analyses using image cameras which may help to get additional information about the characteristic of a measurement surface. In low cost systems additional spacers for touching a surface are often used. But the market is increasingly demanding touchless measurements.

[0011] In alternative solutions, compensation methods may used by providing additional compensation pixel structures that are provided to collect geometry information regarding the incoming irradiation as well as other potential sources of detection errors and to provide those to the sensor control logic in order to modify the spectral compensation matrix for the actual sensor pixels. Summary

[0012] 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 an array of detector elements or pixels , that helps overcome the deficiencies identified above , in particular in a particular lean and simple setup in order to reduce manufacturing costs . Further, an improved multispectral sensor should be provided .

[0013] With respect to the optical detector unit , this obj ect is achieved in that :

[0014] - in addition to the optical sensor, an aperture element is provided, with respect to said substrate , above said optical sensor, said aperture element comprising a flat , laterally extending refractor element defining a top surface and a bottom surface , wherein :

[0015] - said top and bottom surface of said aperture element are provided with a top aperture layer and a bottom aperture layer, respectively,

[0016] - 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 apertures being arranged pairwise , thereby forming a number of double apertures such that in each double aperture the top aperture is arranged on top of its corresponding bottom aperture , and

[0017] - for each of said detector channels , a separate one of said double apertures associated therewith is provided .

[0018] Preferred embodiments are subj ect of the dependent claims .

[0019] The invention is based on the consideration that a signi ficant part of the potential deficiencies mentioned above are considered to be generated by geometry ef fects introduced by the various components . In particular, a main source of errors and inaccuracies in the present consideration is associated with various or all of the sensor channels being provid- ed with one single , common aperture and di f fuser system . 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 single , j oint aperture / di f fuser 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 . 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 .

[0020] In one aspect of the invention, this "one separate aperture per channel" 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 channels . In principle , this "one aperture per channel"-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 .

[0021] 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 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 .

[0022] 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 and the refractive index of the glass . Accurate processes of aperture mask and waver scale mounting in this preferred embodiment guarantee the identical angular power distribution for all spectral channel since these parameters due to high production and manufacturing standards may be provided identically for all channels .

[0023] 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 . In a preferred embodiment , however, the aperture element , with its bottom aperture layer, is directly mounted on top of , preferably even in contact with, the substrate and the optical sensor . In this preferred embodiment , superior alignment of the sensor pixels with their associated double aperture in the aperture element is possible , and due to the direct contact between these components , a very compact design with high mechanical strength may be achieved .

[0024] 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 yet another aspect of the present invention which is considered independently inventive , however, for at least one of the detector channels the optical filter is provided on top of the top aperture of the double aperture associated therewith . In other words , in this preferred setup, the photodiode or pixel of said channel is positioned directly on the substrate , i . e . "underneath" the aperture element covering the substrate , whereas its associated optical filter is positioned on top of the aperture element , and therefore spaced apart from its associated pixel or photodiode by the thickness of the aperture element . In this design, the optical filter, typically and preferably an interference filter, can be processed and structured on top of the aperture element and therefore after mounting of the aperture element as the last process step before dicing .

[0025] In yet another preferred embodiment , an additional block filter may be provided on top of the top aperture of the double aperture of one or more of said detector channels or on top of the optical filter associated therewith . The block filter in particular may be a VIS band pass filter provided to suppress the additional UV and / or NIR ranges of all spectral channels .

[0026] Due to the principal design of the detector unit , homogeneous irradiation of the various channels and their actual sensors as achieved since the channels are provided with individual , associated apertures , and equal conditions for all channels may be provided by appropriate accuracy in manufacturing of the aperture element . Even i f misalignments or the like occurred, the ef fects would be identical for all channels , and no di f ferences between channels would occur . Therefore , as one of the advantages of the present invention, the detector unit, even under high quality and accuracy standards, may be designed without providing diffuser elements as in conventional designs. In principle, such diffuser elements may be considered obsolete in the concept of the present invention since homogeneity among channels is achieved by other means, in particular the "separate aperture per channel" concept. This allows for a very compact design of the detector unit in a miniaturized sensor configuration. In an aspect of the invention, this advantage is expanded further by combining this concept with modern wafer level chip scale packaging ("WLCSP") technologies in order to obtain a reliable, yet cost-effective compact and miniaturized sensor design using only few components. In an aspect of the invention, the detector unit is designed in WLCP technology.

[0027] Depending on the individual application and use case of the detector unit, however, in yet another embodiment of the invention, a diffuser element may be provided, with respect to the substrate, above the aperture element.

[0028] In a preferred embodiment, the pixels each have a different transmission characteristics, preferrably are linearly independent. The pixels can be considered channels of the multi- spectral sensor. 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 different 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 Half Maximum (FWHM) width being approximately equal to the separation between adjacent peaks. In yet another embodiment, the spectral sensitivity of one or each channel may be of Gaussian shape . 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 . The multispectral sensor, in various applications , further may comprise an optical emitter unit , which in yet another preferred embodiment comprises an optical emitter may be arranged in a chamber with an aperture in said housing .

[0029] 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 identical optical and geometrical performance at low tolerances . Therefore , the detector unit , at high accuracy and reliability, may be designed without the necessity to use special di f fuser 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 .

[0030] In other words , according to the concept of the invention, each channel is provided with its own, associated optical aperture . It further is geometrically separated from neighbouring channels , thereby preventing or at least minimi zing cross talk between channels . The channel-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 such as a di f fuser .

[0031] Yet further, due to the channel-wise optical configuration of the 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 toler- ances 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 .

[0032] I yet another advantage , interference ripples may be reduced in IC passivation because of well defined and wide spread of AOI ( FOV) . The filter design may be speci fied for this angular distribution .

[0033] In summary, identical angular power distribution between channels ( as compared to spectral variation by conventional geometrical tolerances in conventional systems ) may be achieved to get similar spectral performance of interference filters . Optical channel separation may be provided by appropriate characteristics of the refractive index of the refractive element . The conventional limitations of filter design rules and necessary compact arrangements of channels may be overcome . In consequence , single spectral channels are suf ficient , whereas in previous systems opposite double diodes to for compensate geometrical , angular and spectral ef fects may be necessary .

[0034] Brief Description of the Preferred Embodiments

[0035] Preferred embodiments and aspects of the invention are described further in connection with a drawing . In this drawing,

[0036] FIG . 1 shows a camera system, in particular for use in a smartphone , FIG . 2 shows an optical detector unit of the camera system of FIG . 1 in cross section;

[0037] FIG . 3 shows an alternative embodiment of an optical detector unit of the camera system of FIG . 1 in cross section;

[0038] FIG . 4-7 each show yet another alternative embodiment of an optical detector unit of the camera system of FIG . 1 in cross section .

[0039] Identical parts are labelled by the same reference numerals .

[0040] Detailed Description of the Preferred Embodiments

[0041] FIG . 1 shows an example of a camera system 1 in cross section that in the embodiment shown is integrated into a mobile device such as a smartphone . It is noted, however, that the concept presented below may very well be uses in other systems or devices , such as wearables . The camera system 1 , as its maj or components , comprises the actual camera sensor system 2 , the details of which are of lesser signi ficance for the invention disclosed here , and an ambient light sensor 4 associated therewith . The camera sensor system 2 and the ambient light sensor 4 are mounted at the back of a common cover glass 6 , which may be the cover glass 6 of the smartphone as such . The ambient light sensor 4 is used mainly for so- called "auto white balance" functionality in the camera system 1 , in order to provide essential background information for appropriate correction functionalities and thereby in general improve imaging quality of the camera system 1 .

[0042] The ambient light sensor 4 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 .

[0043] The optical detector unit 10 of the ambient sensor 4 is shown in enlarged cross-sectional view in FIG . 2 . As shown in FIG . 2 , the optical detector unit 10 comprises a carrier or substrate 12 that 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 as symboli zed by conductor elements 14 .

[0044] As part of the optical detector unit 10 , an optical sensor unit 16 is arranged on the carrier 12 to detect received photons . In this particular embodiment , the optical sensor 16 is integrated into a single semiconductor sensor die 18 together with other electronics . The optical sensor 16 comprises a number of individual optical detector elements or pixels 20 which may be implemented as photodiodes , for example .

[0045] As further part of the optical detector unit 10 , a number of optical filters 22 is provided such that the pixels 20 each are associated with an associated optical filter 22 having a di f ferent transmission characteristic . Together the pixels 20 and associated filter 22 form a detector channel 24 of the optical detector unit 10 . The optical filters 22 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 .

[0046] A control unit and a measurement unit (not shown) are integrated into the semiconductor sensor die 18 alongside with the optical sensor 16 . 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 16 . 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 18 . The semiconductor die 18 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 16 . Each sensor pixel 20 in reaction generates a multispectral sensor signal , respectively . The measurement unit therefore in total provides a set of multispectral sensor signals .

[0047] In conventional sensor units having such detector channels 24 , the substrate 12 with the optical sensor 16 would be arranged in a housing that in order to allow for proper passage of light or radiation, would be provided with an aperture . This aperture would lie within a field of view ( FOV) of the optical sensor 16 . The field of view of the optical sensor 16 includes all points in space from where , at least theoretically, light radiated from an external radiation or light source may traverse towards the optical sensor 16 , e . g . for a fixed detector position and orientation .

[0048] In general , the accuracy and reliability of the output signals provided by the optical sensor 16 may be limited and lowered by a number of factors . In particular, both static and dynamic sources for potential errors in the signals may be of relevance . As an example of static sources for such errors , geometry factors may become relevant . More precisely, the spectral sensitivity of an interference filter based multispectral sensor as used in the embodiment shown depends strongly on the homogeneity of light hitting the respective filters 22 on the detector pixels 20 in order to make sure that the responses of the pixels 20 in relation to each other are constant under varying operation conditions . Considering that the FOV of the optical sensor 16 is limited by the aperture , the relative lateral position of the detectors relative to the aperture is of importance for accuracy . Ideally, the sensor arrangement ought to be concentric with aperture , thereby providing symmetric conditions for all individual pixels 20 . The positioning and its precision, however, may vary and be af fected by di f ferences or tolerances in the packaging process during assembly of the detector unit 2 and the relative alignment of the components , thereby potentially generating variations in amplitude and spectral shape of sensitivity, because of variations in angular power distribution .

[0049] In order to overcome or at least minimi ze such deficiencies , in conventional system a di f fuser would be provided on top or in the area of the aperture in order to increase homogeneity of the incoming radiation . As another source of potential errors or misreadings of the pixels 20 , however, dynamic aspects such as tilt or angular displacement of the sensor arrangement relative to the dominant radiation or light source should be considered as well as ef fects created by the radiation or light source as such . Depending on the performance of an integrated di f fuser, the system accuracy in particular is also depending on the position of a dominant radiation spot or light source . A wide di f fused obj ect will scatter the light more homogeneously into the inside of the detector array than a dominant and small point-type light source . Typically, each di f fuser with a common transmittance ratio has also an ideal Lambertian spread and will also vary the power distribution depending on the position ( tilt vs . detector ) and spectral sensitivity .

[0050] Yet furthermore , the optical filters 22 are characteri zed by spectral transmission characteristics , respectively . In particular, they each have a di f ferent spectral transmission characteristics ; preferably, their transmission characteristics may be linearly independent . Finally, the channels 24 have a spectral sensitivity of their own, may be prone to crosstalk and typically show temperature dependence . A temperature profile of channels 24 may be af fected by ambient temperature , device temperature , emitter temperature and thermal gradients in the optical device . Any of these ef fects may contribute to errors in the generation of sensor signals . In order to overcome these potential deficiencies 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 in a fundamentally di f ferent concept for compensation of such radiance distribution, for increased homogeneity of incoming radiation for the channels 24 , and for spectral reconstruction . In order to achieve such compensation, the detector unit 10 in the embodiment shown, instead of being provided with a j oint aperture shared by all channels 24 , is designed in a "one aperture per channel 24" layout .

[0051] In view of this design goal , the optical detector unit 10 comprises an aperture element 30 provided, with respect to the substrate 30 , above the optical sensor 16 . 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 . 2 facing away from the substrate 12 carrying the sensor unit 16 , and a bottom surface 36 , in the mounted state shown in FIG . 2 facing towards the substrate 12 carrying the sensor unit 16 .

[0052] 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 is selected, 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 . 2 , 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 of a corresponding bottom aperture , 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 , e . g .

[0053] As can be seen In FIG . 2 , for each of the detector channels 24 , a separate one of the double apertures 46 associated therewith is provided . Thus , the embodiment shown provides a detector unit 10 designed with a channel-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 comprises this aperture element 30 in addition to a TSV chip with photodiodes providing the sensor pixels 20 . The FOV for each channel 24 , and accordingly the associated pixel 20 , is defined by the diameter of the associated apertures 42 , 44 on first and second aperture layer 38 , 40 on glass 32 and IC, the thickness of the glass 32 , and the refractive index of the glass 32 . This is indicated by arrows 48 indicating the limiting rays of the respective FOV of the individual channels 24 ; as shown in FIG . 2 , due to the refractive ef fects of refractor element 32 , the direction of propagation of these rays changes at surface 34 of the refractor element 32 . Accurate processes of aperture mask and wafer scale mounting, as widely available , guarantee the identical angular power distribution for all spectral channels 24 . In particular, the channel-wise optical separation defines a similar optical performance ( FOV, synchronic alignment , power distribution on filter, etc ) for all colour or spectral channels 24 without an additional optic .

[0054] In a lateral perspective , the channels 24 comprising the respective sensor pixels 20 and also the associated double apertures 46 , may be positioned in relatively large distances from each other, leaving relatively large gaps in between . This freedom of positioning, made possible by the concept of assigning individual apertures to each channel 24 , allows for ef ficient use of the chip ' s surface area since electronic components , circuitry, etc, may be placed into the gaps between channels 24 . Furthermore , optical cross talk between neighbouring channels 24 may be blocked by a defined minimum distance between the channels 24 . 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 .

[0055] The aperture element 30 may be positioned in some distance away from the substrate 12 carrying the sensor unit 16 , thereby forming a gap between the top surface of the substrate 12 and the bottom aperture layer 40 of the aperture element 30 . In a preferred embodiment as shown in FIG . 2 , and in accordance with one aspect of the invention, however, the aperture element 30 , with its bottom aperture layer 40 , is directly mounted on top of the substrate 12 and the optical sensor unit 16 . In this configuration, the aperture element 30 in the way of an additional functionality also serves as protection and cover for the sensor unit 16 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 16 , which typically is designed as a mold or an overmold . Beyond increased mechanical strength and durability provided by the aperture element 30 in this function, in comparison with the typical overmold the aperture element due to the basic material of glass tends fer significantly less aging properties, and also lessened temperature dependence.

[0056] As mentioned, each channel 24 in addition to the photodiode or pixel 20 comprises an optical filter 22 associated therewith. In the embodiment shown in FIG. 2, the optical filter element 22 is positioned directly on top of the associated pixel 20. In another embodiment and yet another aspect of the invention, however, the optical filter 22 may instead for at least one of the channels 24 be provided on top of the top aperture 42 of the double aperture 46 associated therewith. This preferred embodiment is shown for the alternative optical detector unit 10' shown in cross section in FIG. 3. In other words, the interference filter 22 (single or stacked) can be processed and structured on chip or top on the glass 32. In the embodiment of FIG. 3, the filter 22 can be processed after glass mounting as the last process step before dicing. This is considered highly beneficial and efficient and reduces additionally the effective interference ripples also for more paraxial light applications without a diffuser.

[0057] In yet another preferred embodiment, as shown in cross section in FIG. 4, the optical detector unit 10' ' may comprise an additional block filter 50 provided on top of the top aperture 42 of the double aperture 46 of one or more of the detector channels 24 or on top of the optical filter 22 associated therewith.

[0058] Due to the design concept "individual aperture for each channel 24", the detector unit, even under high quality and accuracy standards, may be designed at low cost, with only few components, and in miniaturized way, in particular in a highly preferred combination with modern wafer level packaging technologies, without providing separate diffuser elements as in conventional designs. Depending on the individual use case of the detector unit 10, however, in yet another embodiment of the invention, a diffuser element 52 may be provided, with respect to the substrate 12, above the aperture element 30. This embodiment is shown in cross section in FIG. 5. The dif fuser element 52 in principle may be positioned at any convenient height above the aperture element 30 ; with respect to geometry, the lateral si ze of the di f fuser element 52 ought to be big enough to cover the full FOV of the individual channels 24 .

[0059] In yet another embodiment , as shown in FIG . 6 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 allow to add direct di f fuser on top .

[0060] In the embodiments shown previously, the detector unit is designed in miniaturi zed manner, yielding a high package density . In an alternative embodiment , however, the concept of "individual aperture for each channel 24" may also applied for more conventional geometries . FIG . 7 , in cross section, shows yet another alternative embodiment of an optical detector unit 10 ' " ' ' . In this embodiment , the ensemble of substrate 12 with sensor unit 16 and covered by aperture element 30 is positioned within a housing 54 with a sensor chamber 56 . In order to allow for proper passage of light or radiation to reach the sensor unit 16 through the housing 54 , the housing 54 is provided with an opening or aperture 58 in a cover section or lid 60 of the housing 54 .

[0061] The embodiments of the optical sensor device 1 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 , modifications , 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 .

[0062] 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 .

[0063] 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 .

[0064] 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 .

[0065] 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 .

[0066] LIST OF REFERENCE NUMERALS camera system camera detection system ambient light sensor cover glass optical detector unit substrate conductor elements sensor unit sensor die pixel optical filter channel aperture element refractor element top surface bottom surface top aperture layer bottom aperture layer top aperture bottom aperture double aperture arrow block filter di f fuser element housing sensor chamber aperture lid

Claims

CLAIMS1. An optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') comprising :- an optical sensor unit (16) arranged on a substrate (12) to detect received photons, said optical sensor unit (16) comprising a number of sensor pixels (20) each generating a mul- tispectral sensor signal as part of one of a number of detector channels (24) , respectively, and- an aperture element (30) provided, with respect to said substrate (12) , above said optical sensor unit (16) , 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) such that in each double aperture (46) the top aperture (42) is arranged on top of its corresponding bottom aperture (44) , and- for each of said detector channels (24) , a separate one of said double apertures (46) associated therewith is provided.

2. The optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') of claim 1, in which said refractor element (32) is a glass element .

3. The optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') of any one of claims 1 to 3, in which said aperture element (30) , with its bottom aperture layer (40) , is directly mounted on top of said substrate (12) and the optical sensor (16) .

4. The optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') of any one of claims 1 to 3, in which each of said detectorchannels (24) comprises at least one of said pixels (20) and an optical filter (22) associated therewith.

5. The optical detector unit (10, 10', 10' ', 10' ' ', 10' ' ' ') of claim 4, in which for at least one of said channels (24) the optical filter (22) is provided on top of the top aperture (42) of the double aperture (46) associated therewith.

6. The optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') of claim 4 or 5 comprising an additional block filter (50) provided on top of the top aperture (42) of the double aperture (46) of one or more of said detector channels (24) or on top of the optical filter (22) associated therewith.

7. The optical detector unit (10, 10', 10' ', 10' ' ', 10' ' ' ') of any one of claims 1 to 6, further comprising a diffuser (52) provided, with respect to said substrate (12) , above said aperture element (30) .

8. The optical detector unit (10, 10", 10" ', IO' '", 10' ' ' ') of any one of claims 1 to 7, in which the channels (24) each have a different spectral transmission characteristic.

9. The optical detector unit (10, 10', 10' ', 10' ' ', 10' ' ' ') of claim 8, wherein the different transmission characteristics of the channels (24) are linearly independent.

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

11. The multispectral sensor of claim 10, which is designed as an Ambient Light Sensor (4) .

12. Camera system (1) comprising an ambient light sensor (4) having an optical detector unit (10, 10", 10" ', IO' '", IO' ' ' ') of any one of claims 1 to 9.

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