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n+/psub (native) ESD diodes

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rubink

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Typically ESD diodes to ground will be n+ in Pwell, but in a process with native option n+ in psub without the Pwell implant is an alternative.
This can have lower junction capacitance so would seem useful for a lower capacitance ESD diode.
Are there any disadvantages for these diode types for ESD protection?
 

dick_freebird

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Higher series resistance is one issue. You need to hold down
voltage and your only way to beat down Rs is width. Though
the high resistivity diode will show more conductivity modulation
it will never catch up. There could be a few tens of mV bonus
in lower Vf (if that is indeed a bonus and not a substrate noise
injection increase hassle instead).

Needing more width may defeat your interest in lower C.
 
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    rubink

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rubink

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OK thanks. In ESD Symposium 2002 paper "Optimization of Input Protection Diode for High Speed Applications" they found that n+/psub diodes were indistinguishable
from n+/Pwell diodes at high injection but they did highlightlight other issues.
 

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