When do we draw NFET on the p-well and when on the n-well in the layout?

[dongqing]

Hi guys:

Usualy we draw nfet on the p-well in the layout

but sometimes we need draw nfet on the n-well

then what't the condition? and why?

Thanks in advance!

dongqing

 

[cmos_dude]

NFET in the layout

An NFET in an NWELL is used to have Capacitors in the layouts. Such MOSCAPS are used because the have less fringing effects and also high Cap when compared to an MIM cap

--cmos_dude