Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

ESD protection diodes/SCR layout

EEcrazy

Newbie
Joined
Oct 29, 2010
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,346
Does this layout for finger ESD protection diode make any sense? What is the reason for adding n-well right under the n+ contacts?
Or may be I have p&n backwards, so its actually SCR?
Thx!
diodes.png
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
7,415
Helped
2,154
Reputation
4,313
Reaction score
2,028
Trophy points
1,393
Location
USA
Activity points
59,366
DN+ will raise the junction breakdown and force some other region into play. Such as channel reach-through or allow some better controlled trigger. Could also be that if unprotected that drain would become the current- crowding point of failure at over-the-top ESD levels.

Question whether this is truly a SCR or just a GGNMOS snapback clamp, the turning and turnoff are way different.
For SCRrs you need to take care about the turnoff, you want a GTOSCR that will absolutely turn off under all valid powered application conditions. If a logic level input can keep a SCR lit then you have an angry customer problem.

Device design has a huge impact on gate-turnoff ability and this is the province of old-timey tricks and in-fab cut-and-try (been there, got the patent).
 

EEcrazy

Newbie
Joined
Oct 29, 2010
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,346
Thanks. I don't believe it is a GGNMOS, there are no poly gates anywhere near ESD protection. That N well also extends under the bond pad itself, but not quite all the way. Would not it just form a large area nwell to substrate diode? Here is what it looks like, both p+ fingers and p+ guard ring connect to ground.
diodes2.png
 

LaTeX Commands Quick-Menu:

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top