Metal-gate resistance with skin effect consideration in nanoscale MOSFETs for millimeter-wave ICs

Copper metal gate has been introduced in logic CMOS processes starting from the 45-nm technology node. With the skin depth of about 270 nm at 60 GHz for copper, the DC end-to-end resistance of the copper gate electrode is found to be R_dc ≈ 9 Ω for a 45-nm MOSFET with W/L = 30 and it is a good estimation of the actual effective resistance R_ac with less than 1% error. R_ac of copper-gate electrode with rectangular cross-sectional designs is investigated with skin effect consideration. Design guidelines are suggested for device optimization of nanoscale metal-gate MOSFETs for millimeter-wave integrated circuits.