Different Diodes in CMOS technology?

[katrin]

The design kit (CMOS AMS) provides three different kinds of diodes

1, nwell on Psubstrate
2, p diffusion on Nwell
3, n diffusion on Psubstrate

Now I want to design ESD protection circuit, therefore, i need to implement the diodes
from pad to Vdd and ground.

I am confused about which diode can I select ?

At the same time, the design kit offers just the symbol. but no layout for the diodes. Do I need to draw the layout by myself, or can I ask the foundry for help?

 

[littlej_zju]

Usually, P+/Nwell is used for Vdd-Vss ESD protection diode. For P+/Nwell diode, Nwell tied Vdd and P+ tied gnd, thus there is minimum leadage between Nwell and Psub (tied gnd).
As for layout, you can ask foundry to provide examples.