Layout : MIMCAP and MOSFET

[gradha]

Hey ,
Guys i am using TSMC130 i have a issue using mimcap (top metal 6) as i am not using metal5 or metal6 anywhere else in the layout is there a chance of placing the mimcap above the mosfet what could be the problems that i could face atmost. and also consider the cases such as below
what if moses array are of three kinds
1. Normal mosfet
2. Current mirror
3. differential amplifier.

And for just to clarify i already tried it and the layout is clean from DRC and LVS issues and matching the schematics or netlist.

Thanks and Regards
Govind.

 

[erikl]

No problem. In order to not increase mismatch, you should cover corresponding transistors (item 2. and 3.) equally.

 

[Teddy]

I suppose you are not in the industry but at school. If not - you can save some $$$ by using M5 MiMcap. To me if you are not using 6 metal layers then drop the MIM down.
If you are ok with extra metal - you can always cover whole area under the MiM with metal connected to GND in order to provide uniform "background" for the MiM. Those caps are extracted in ideal environment (with no structure under) and their value might not be exactly what you expect when put above active circuitry. Also the matching of anything bellow will change.
If you cover all the structure under the Mim with uniform GND connected metal matching will be fine, MiM will be fine - it's a win win