Purpose of Double Guard Ring than Single Guard Ring

[B_hawk]

Hi friends,

Can any one please tell me the reason for using double guard ring (i.e.PTAP,NTAP) in a block which has both PMOS and NMOS.

Thanks,

Karthik

 

[dick_freebird]

Concentric guardrings are common in ESD related circuitry
(pad cells etc.). One useful function is that the built-in
depletion region is a "getter" for loose minority carriers in
the substrate. The ring can also kill lateral BJTs' base
ohmically and deterministically if it is closed / pervasive,
fight field oxide inversion / charging and so on.

Cost sensitive folks might find it uneconomical but "must
not fail" folks see it as another dose of tonic.

 

[B_hawk]

Hi,

Thanks for your response. Is there any material regarding this? That ill b better to know more about guard ring. kindly share it if you have any documents.

Regards,

Karthik