in which metal layer core power ring should be formed?

[shavakmm]

i have 6 metal layers available M1 to M6. My design is block level. The general idea is to have core power ring using higher metal layer due to its less resistance. Power rails are normally laid down in lower metal layer M1. If core ring and rails have to be connected then vias V12, V23, V34, V45, V56 have to be used which may pose reliability problems. Friends what you people think? Which layers are best for core power ring formation? What will be the affect of this on IR drop ?

rgds
murali
https://asic-soc.blogspot.com

 

[rookie3]

Hi Murali,

Normally we use the low-resistivity metals (which will be M5, M6 in your process), for the power and ground lines. This is in order to minimise the IR drops, of course.

 

[armardu]

m5 or m6