blue MTF rolloff

[geary%cfa3.DECNET at cfa.harvard.edu]

Yes, I am afraid that MTF degradation in the blue will be with us
for the present generation of CCDs from the UofA shop.  Mike Lesser
stops his process at about 15 microns thickness or so, I believe,
which is a bit beyond the depletion depth for the silicon used (30-
50 ohm-cm).  So, after UV flood, when the production of collected
blue photons near the back surface is enhanced, you will probably
see a softening of MTF.

Solutions:
(1) thin to 10-12 microns.  But be aware that red fringing is likely
to be magnified, perhaps considerably.
(2) Use hi-resistivity epi (100+ ohm-cm). Hard to get in proper
quality, and may introduce processing problems on the fab line (it
has in the past).  Might allow much-reduced red fringing (thicker
device) while still preserving blue MTF.

--John Geary
                               ,,,
                              (o o)
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  "When you are up to your ears in it, keep your mouth shut."

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