Hi Henry
At cell level I generally route both VDD and GND in Metal 1 horizonally, this means I can tap directly into my current mirrors, guard rings etc. I then use metal 2 exclusively for vertical routing and metal 3 for horizontal. It would be nice to use metal 1 exclusively for horizontal, but the prevelance of guardrings etc generally makes that an awkward strategy.
Pat, what i m getting from this is that you are using metal 1 as main branch and metal 2 and 3 as subbrances for power routing...
I think this is not the best way..... both current handling and parasitic of higher metal(2 and 3 ) is better.... so i think we should use metal 3 and metal 2 as main supply.....
Let me know your views.