[SOLVED] routing with metal layers over MOS

[shriraj19]

i am lay-outing an OTA which is a critical block for and 16-bit ADC.
can i route with metals over MOS, to save area?

 

[kenambo]

Hi,

Actually I cant understand your question..

but, i can tell some tips regarding metal routing..

You can route metals over MOS but you should not touch or short the MOS terminals with the SAME mETAL.. fOR EXAMPLE, IF you use metal1 means u cant draw over mos becuase the drain and source of the mos covered with metal1 so u can use metal 2 and others,, no problem to route over MOS..

HOpe u understand this.. and Any doubt ask me..

 

[shriraj19]

but i heard that for critical analog and rf circuits the metal over poly should be avoided????

Hi,

Actually I cant understand your question..

but, i can tell some tips regarding metal routing..

You can route metals over MOS but you should not touch or short the MOS terminals with the SAME mETAL.. fOR EXAMPLE, IF you use metal1 means u cant draw over mos becuase the drain and source of the mos covered with metal1 so u can use metal 2 and others,, no problem to route over MOS..

HOpe u understand this.. and Any doubt ask me..

 

[mjoyner]

but i heard that for critical analog and rf circuits the metal over poly should be avoided????

typically true for metal 1 & metal 2. parasitic extract and sim to ok/verify metal 3 and higher

 

[okguy]

Routing with metal 1 or 2 will affect dopings in gate or drain/source and obviously add parasitic capacitances.
From Metal3 and above, it affect only parasitic capacitance. So, we avoid such routing.
In some case, those effects are not critical if your amplifier is not critical ...

 

[gradha]

yeah u can do it but make sure that u don't route metal1.
From metal2 and above will be fine and also while routing keep in mind that u should'nt use vias (any vias) above the active(PO+OD) area. If u place a via above active it effects the Vt of the mos, which is critical.