Why NMOS has snapback properties

[bicave]

nmos + snapback

I wonder how NMOS can have snapback,
ESD so complicated! I don;t know its behavior. Do you have any material illustrate it more clear.

Thanks

 

[pbs681]

snapback nmos

NMOS transistor has parastic BJT npn. During snapback, this BJT transistor that conducting the current. So, the snapback current is actually a parasitic BJT current

 

[ssuchitav]

nmos snapback

Is this BJT current is triggered by high electric field near the drain junction? which is so called J-E heating?

 

[jordan76]

Some explanations:
Due to high electric field at NMOS drain, electron-hole pairs are generated as a result of avalanche break-down, then parasitic BJT is triggered when source-substrate junction is forward-biased.

I assume you are referring to joule-heating by "J-E heating": the power consumed by Rsub of parasitic BJT.

Hope it helps.

Regards,
Jordan

 

[leebluer]

It perhaps before snapback only BVds affect; while P-sub current cause parastics NPN BE junction conduct, parastics NPN affect. Vce is smaller than BVds.