ST Micro application US20090014764 talks about improving BSI sensor crosstalk. To achieve this, ST goes beyond silicon and uses SiGe alloy in the photodiodes to improve red light absorption, thus reduce the layer thickness and so reduce the crosstalk, mostly in green and blue. Having very thin photosensitive layer also opens other isolation possibilities, such as oxide-filled shallow trenches.
Aptina application US20090017573 proposes a dual or triple Vth transistor in the pixel source follower to modify its sub-threshold behavior and extend the output voltage swing. The extension is not large and does not justify the additional Vth adjust mask, in my opinion. But if just a combination of existing masks is used, it might be worth considering.
Siliconfile application US20090014761 proposes to extend the photodiode under field oxide region to improve fill factor. This idea has a lot of prior art from Aptina, Sony, Omnivision and many others. I don't think it would be granted.
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