ESD diodes: do they need any guardring ?

[DoYouLinux]

esd guard ring

Hi all,

I am trying to design my own ESD protection pads using two basic diodes. Do I need to place any guardring close to the diodes. My diodes are Nwell diodes.

Thank you very much

DYL

 

[Fom]

esd double diode esd substrate connection

You need the guard ring to prevent latch-up problem.

 

[hung_wai_ming@hotmail.com]

guard ring

Fom is right

 

[DoYouLinux]

need of guard ring

Thanks a lot, Fom and hung wai ming

By the way, for the guard ring, should it be the "P-tap" connected to the "Ground" ?

 

[mdcui]

how+guard+rings+help+in+esd

usually for ESD device, you need guard ring, and some times even double guardring for two reason:
1. guard ring with enough contact and metal connection can help distribute ESD zapping current, sometimes current flows more through the guardring than from the substrate.
2. isolate the noise introduced by the diode under normal operation, since IO signal may easily have negative glitch, and will introduce noise into substrate without guardring the collect the carrier current.

but the distance of double guardring need to be controlled well since it can easily form a collateral npn transistor. and without enough conatct or strong metal power bus on top of metal ring, it will be less effective.

 

[DoYouLinux]

guard ring esd diodes

Thank you very much, mdcui

For double guarding, you mean, one is "p-sub" contact connected to ground and the other one is "n-well" contact connected to Vdd, right ? If so, for the latter one, I need to draw N-well all around the diodes and connect the N-well to Vdd. Am I correct ?

 

[engrak]

back to back diodes in esd

i think u r correct.