Wednesday, March 30, 2011

Omnivision Proposes Contact Dummy Pixel

Omnivision's recent patent application US20110068429 talks about providing the contact to the backside of BSI pixel array. Ideally, these contacts could be placed inside each pixel in the array. For small pixels this requires hard trade-offs in the pixel layout. Hence Omnivision proposes to sacrifice a small number of pixels for dummies having backside contacts like this:


The application talks about devoting one pixel in thousand to such a backside contact (one in each 32 x 32 block, or, may be, pseudo-random). The application says that "already established and applied methods of averaging out white or dead pixels in any CIS device will also remove the impact of the contact-dummy pixels from the final image. Therefore the final image will not significantly be altered by contact dummy pixels."

8 comments:

  1. If they chose to implement this, anyone with access to enough die should be able to figure out which and how many pixels are dummys.

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  2. The description in the blog appears incorrect -- the purpose of this is for FSI with a buried n-well. The substrate 305 and layers 307 & 310 would block BS illumination.

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  3. this is so obvious i don't even think i ever wrote it down on the several occasions i considered it as a suitable solution

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  4. @ "The description in the blog appears incorrect -- the purpose of this is for FSI with a buried n-well."

    The application's text specifically talks about BSI problem it goes to solve. For example:

    "FIG. 3 illustrates how a contact dummy pixel can be applied to a vertical overflow drain (VOD) structure of a BSI CIS pixel architecture, in accordance with an embodiment of the invention."

    I'd guess the figures show BSI structure before the substrate is removed.

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  5. A so-called, dummy pixel has already been done by others.

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  6. The n collector layer (310) should be eliminated for BSI and so the dummy pixels will not work. I still think this scheme could have some benefit for FSI.

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  7. This is exactly the internal structure of BCCD. The N collector can be used for reseting the PD and also as an antiblooming vertical channel.

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  8. I think this application interferes with a few of the patent apps Omnivision just bought.

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