Light-sensing array with wedge-like reflective optical concentrators

{
  "publication_number": "US5952645A",
  "country": "US",
  "kind": "A",
  "title": "Light-sensing array with wedge-like reflective optical concentrators",
  "abstract": "Wedge-shaped optical reflectors are used to reflect optical energy. Certain optical energy is incoming toward an area of the chip that is housing the non-photosensitive electronics. Wedges are used to reflect that radiation toward the photosensitive electronics.",
  "claims": [
    "1. An optical detector, comprising: an image receiving surface formed on a semiconductor substrate, including at least a photosensitive area and an adjacent non-photosensitive area and operating to receive light incident upon said detector from the side of said imaging receiving surface; and a light collecting element formed over said image receiving surface relative to said photosensitive area and said non-photosensitive area and configured to couple said incident light to said image receiving surface by reflection and to enhance a light-collecting efficiency of said photosensitive area and imaging resolution without a lensing operation or an operation of total internal reflection, wherein said light collecting element includes at least two light reflecting surfaces, adjacent said photosensitive area and each forming an acute angle with respect to a normal direction of said image receiving surface, said light reflecting surfaces operable to reflect at least a portion of light which would otherwise impinge on said non-photosensitive area towards the photosensitive area, wherein said two light reflecting surfaces are configured to reflect certain light rays that are incident towards said image receiving surface at an incident angle larger than a prespecified incident angle away from said image receiving surface.",
    "2. A detector as in claim 1 wherein said photosensitive area includes a photogate and said non-photosensitive area includes an area of the substrate integrating an amplifier associated with the photogate.",
    "3. A photodetector, comprising: a substrate, including a sensing surface which has a first photosensitive area and a second non-photosensitive area; and a reflective element formed on said sensing surface and located in a location to reflect at least a portion of incident radiant energy incident to said substrate from said sensing surface side that would otherwise impinge on said second area to said first area, without a lensing operation or an operation of total internal reflection, wherein said reflective element is configured to reflect certain light rays that are incident towards said sensing surface at an incident angle larger than a prespecified incident angle away from said sensing surface.",
    "4. A photodetector as in claim 3, wherein said substrate includes an active pixel sensor.",
    "5. A method of acquiring radiation over an area, comprising: positioning a radiation sensitive element formed on a receiving surface of a semiconductor substrate to receive radiation; and using at least one reflective surface of a wedge-like structure having a plurality of reflective surfaces and formed on said receiving surface to reflect at least a part of the radiation that is incident in a direction where said part would not impinge on said radiation sensitive element, toward said radiation sensitive element, without a lensing operation or an operation of total internal reflection, using at least two of said reflective surfaces to operate in combination to reflect certain light rays that are incident towards said receiving surface at an incident angle larger than a prespecified incident angle away from said receiving surface.",
    "6. An optical detector, comprising: a semiconductor substrate having a first side and a second opposite side, said first side having a sensing surface configured to receive radiation incident to said substrate from said first side; a plurality of detector pixels formed on said sensing surface as a sensing array, each detector pixel including a radiation-sensitive area and a non-radiation-sensitive area; and a light coupling array formed on said sensing surface atop of said detector pixels and comprised of a plurality of micro-wedges having straight edges that form radiation-receiving openings to continuously connect to one another without gaps so that any radiation ray incident to said light coupling array is received by one of said radiation-receiving openings, wherein each micro-wedge has a base and at least two reflective surfaces that respectively intersect said base to form an acute angle with respect to a normal direction of said base and is positioned relative to said radiation-sensitive area so that said reflecting surfaces direct at least a portion of said radiation incident from said first side that would otherwise impinge non-radiation-sensitive areas to respective radiation-sensitive areas, without a lensing operation.",
    "7. A detector as in claim 6, wherein each said micro-wedge is formed on top of a respective non-radiation-sensitive area by at least partially overlapping said base with said respective non-radiation area and two adjacent micro-wedges are displaced from each other to expose a respective radiation-sensitive area to said first side of said substrate.",
    "8. A detector as in claim 7, wherein said reflective surfaces are coated with a radiation-reflective material.",
    "9. A detector as in claim 6, wherein said micro-wedges are configured to have a specified ratio of a height over a width of said base so as to reflect certain radiation rays, that are incident towards said sensing surface from said first side at an incident angle larger than a prespecified incident angle, away from said sensing surface.",
    "10. A detector as in claim 6, wherein each micro-wedge is formed of a material that is at least partially transparent to said radiation and is located on top of a respective radiation-sensitive area and a facet opposing said base of said micro-wedge covers said respective radiation-sensitive area so that said reflective surfaces of said micro-wedge direct at least a portion of radiation rays entering said micro-wedge from said base onto said respective radiation-sensitive area.",
    "11. A detector as in claim 10, wherein bases of two adjacent micro-wedges are in contact with each other.",
    "12. A detector as in claim 10, wherein each micro-wedge is configured so that said reflective surfaces reflect at least a portion of said radiation rays entering from said base by total internal reflection.",
    "13. A detector as in claim 6, wherein each photosensitive area includes a photogate and the respective non-photosensitive area includes an area of said substrate integrating an amplifier associated with said photogate.",
    "14. A detector as in claim 6, wherein said two light reflecting surfaces are configured to reflect certain light rays that are incident towards said sensing surface at an incident angle larger than a prespecified incident angle away from said sensing surface.",
    "15. An optical detector, comprising: a sensing array of detector pixels formed on a semiconductor substrate and operable to convert photons into electrical signals, each detector pixel including a radiation-sensitive area and a non-radiation-sensitive area; and a light coupling array formed over said detector pixels and comprised of a plurality of coupling elements having straight edges that form radiation-receiving openings to continuously connect to one another without gaps so that any radiation ray incident to said light coupling array is received by one of said radiation-receiving openings, each coupling element having at least two reflective surfaces and positioned relative to said radiation-sensitive area so that said reflecting surfaces direct at least a portion of incident radiation that would otherwise impinge non-radiation-sensitive areas to respective radiation-sensitive areas, wherein said two light reflecting surfaces in each coupling element are configured to reflect certain light rays that are incident towards said sensing array at an incident angle larger than a prespecified incident angle away from said sensing array.",
    "16. A detector as in claim 15, wherein one reflective surface of one coupling element intercepts another reflective surface of an adjacent coupling element so as to cover at least one non-radiation-sensitive area of one detector pixel.",
    "17. A detector as in claim 15, wherein said reflective surfaces are curved.",
    "18. A detector as in claim 15, wherein said detector pixels are active sensing pixels and each non-photosensitive area includes an amplifier."
  ],
  "description_excerpt": "The present invention describes control of channeling of light in a pixel-sensing device.\n\nActive Pixel Sensor (\"APS\") technology represents a second generation image sensor technology. An Active Pixel Sensor includes image acquiring structure, including an amplifier, in each pixel.\n\nEach pixel has a limited light gathering capability that is proportional to the size of the light gathering structure. However, this image acquiring structure has previously taken up some of the otherwise availible area, or \"real estate\" on the image sensor substrate, \"the chip\". The so-called \"fill factor\" is a measure of how much of the chip is used to gather incoming light. Fill factor is degraded by this associated image acquiring structure. The fill factor of active pixel sensors has been as low as 20 to 30 percent.\n\nOne possible solution to this problem is the use of microlenses, such as described in co-pending patent applications, e.g. Ser. No. 08/558,521. Microlenses have been used in an attempt to refract some of the light impinging on the active pixel sensor to a photoreactive location. For example, if the light impinges on an area of the real estate that holds the amplifier, that light may be refracted to the area of the photosensitive element.\n\nHowever, the inventors noticed problems with using the microlenses.\n\nThe shape of the microlens is very difficult to control. Rays having large incident angles may be shifted to the neighboring pixels by the microlenses. The inventors hence found that introducing the microlenses may increase the crosstalk and noise level.",
  "cpc": [
    "H10F 39/8063",
    "H10F 39/8067",
    "H10F 77/413"
  ],
  "ipc": [
    "H01L 31/0232"
  ],
  "assignees": [
    "California Institute of Technology"
  ],
  "inventors": [
    "Yu Wang",
    "Eric R. Fossum"
  ],
  "filing_date": "1996-08-27",
  "publication_date": "1999-09-14",
  "grant_date": "1999-09-14",
  "priority_date": "1996-08-27",
  "application_number": "US-70807596-A",
  "family_id": "24844289",
  "cited_by_count": 65,
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}