help:devices underneath mim caps

[viyag]

hi,
I want to put devices under mim caps,
but how to calculate the parastic parameters,
and how to do in the lvs and rcx?
what should i pay more attention ？
ｔｈａｎｋｓ

 

[transbrother]

viyag,

You'd have to first determine what kind of devices you want to put underneath your mim caps. for e.g. i would never put input pairs and matched elements underneath these caps because they would affect the matching performance. At the same time, i would not put any switching circuitry underneath the mim caps as it might couple and affect the cap performance.

Calculation of parasitic parameters will be difficult and will depend on the circuit element you put underneath the caps. For e.g. if you have poly underneath then you'd have to check for mim bottom plate cap metal to poly capacitance; if you have some nwell underneath then nwell to metal cap, etc etc. Your best bet is to do some parasitic extraction to get an easier answer.

As far as LVS, you shouldnt in theory have any issues just by having devices underneath because you are not making any inadvertent connections.