Saturday, October 10, 2009

Omnivision BSI Pixel Crosss-section Revealed

WIPO published Omnivision patent applications WO/2009/099778 and WO/2009/100039 on BSI photodiode profile and WO/2009/100038 on black pixels in BSI technology. While the black pixel idea is quite obvious - removing photodiode implants to make black pixel light-insensitive, a really interesting part of these applications is Omnivision BSI pixel cross-section:


One can see that the photodiode extends well underneath the transistor region. Apparently, Omnivision did a great job to achieve lag-free operation with such a complex shape of the fully depleted photodiode.

The earlier Omnivision BSI applications, such as WO/2009/099483, WO/2009/09949, WO/2009/099494, WO/2009/099491 do not mention the extended photodiode profile. By the way, the last of these has an interesting part describing optimizations of the backside implant and the sensor's substrate thickness.

8 comments:

  1. A patent application does not necessarily mean that the idea is present in the products ....
    A.T.

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  2. True. However, if the same idea appears in 3 applications on different aspects of BSI pixel, there should be something in it. For example, the black pixel application has only extending PD pictures. It describes p- and n-type versions of PD, but they both have the same extending deep portion.

    I hope Chipworks can say something more definite about it, they have a complete reverse engineering report on Omni BSI sensor.

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  3. interesting typo I guess in 099494, where they talk about a suiciding layer instead of a siliciding layer. A.T.

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  4. Those are old US patents.

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  5. Yes, the patent applications are from 2008. However, they are published only in August 2009, two months ago. In that sense they are quite new.

    A.T. - funny typo!

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  6. Fig.4 : Very difficult structure to make it fully depleted. I assume PD is implanted from the back to make the PD profile a shallow sandwich. The question is how much is the bridge doped to extract all electrons? Or they can leave with N+ and a few e- kTC? The lag could be flushed out...

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  7. how can you aneal the deep-diode if it is implanted from back-side?

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  8. Oh, that's easy. First you need to switch Cu interconnects for carbon nanotubes. Then switch MOSFETs for silicon-carbide JFETs and bipolars. Then you can do whatever annealing you want. Most important, don't forget to move CF and ulens till after annealing step.

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