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Why use N+ diffusion resistor as ESD protection?

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020170

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diffusion resistor

some ESD circuit uses N+ diffusion resistor.

N+ diffusion resistor has smallest sheet resistance among the resistors in the process.

High resistance poly resistor has very large sheet resistance, it's very useful.

but Why do I have to use N+ diffusion resistor instead of High resistance poly resistor as ESD protection resistor?


thanks.
 

why use a diffusion resistor

1) High current capability of diffusion resistor in comparison with poly resistor.
2) Diff. resistor has an feature, it can limit current due to velosity saturation effect. So max. current is depended on the resistor cross section.
3) High resistance in signal path gives u increased delay for signals.
 

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    020170

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poly resistor and diffusion resistor in esd

But diffusion resistor has parasitic diode. It will influnce the ESD performance.
 

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diffusion resistor vs poly resistor

gsheng said:
But diffusion resistor has parasitic diode. It will influnce the ESD performance.
Click to expand...

Is it better ESD effect if you use N+ diffusion resistor?

In my thought, if some negative ESD voltage come into PAD, diode that was consisit of N+ & p-sub protects internal Circuit from negative ESD voltage.

Am I wrong?
 

n- diffusion resistance tc

In my thought, if some negative ESD voltage come into PAD, diode that was consisit of N+ & p-sub protects internal Circuit from negative ESD voltage.

Am I wrong?
Click to expand...

Yes. You are right!

The resistor combined with the parasitic diode will help the ESD performance.

Indeed, they form the secondary ESD protection circuit.

This technique is common used.

Yibin.
 

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poly resistor for esd purpose

This N+ diffusion diode to Psub can create latchup during ESD events. Poly might be better in those cases
 

use resistor esd

Diffusion resistor can spread heat very quickly while poly resistor can not since oxide is arround poly. Poly resistor is more easy to be burnt than diffusion resistor at ESD zapping.
 

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diffusion resistor

I agree the point lianggu said. poly resistor is more easy to be demolished by the ESD thermal. We know a ESD device must protect itself from ESD current first,and then it can protects others more.By the way,N-well resistor welcomed in ESD.
 

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diffusion resistor in well

lianggu said:
Diffusion resistor can spread heat very quickly while poly resistor can not since oxide is arround poly. Poly resistor is more easy to be burnt than diffusion resistor at ESD zapping.
Click to expand...

"oxide is arround poly", you mean "Filed Oxide"?
 

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