Too bad the article is lacking on the technical details. This is about energy efficiency, not GHz. They have hit 4GHz and higher with a traditional clock mesh. The point here is that they hit 4GHz with a resonant clock mesh. What this means is that instead of charging and discharging the huge capacitor that is the clock grid every cycle using only FETs connected to VDD and VSS (traditional digital logic), there is an LC tank circuit that is resonating with the clock grid. The power rails still do some of the charging and discharging of the grid, but now some of the energy comes from the oscillator. I have seen the paper, the distributed LC tank is pretty cool. The technical achievement is that they got this to run at 4GHz while keeping the skew between clock grid points as low as a traditional mesh (had the skew increased, the max frequency of the processor would go down). They claim reduced clock power of 25%. Given that clock power is roughly half the power of a core, that's a 12% power reduction overall, pretty impressive. It's also really cool that the whole thing is on-die - they made the inductors out of back-end wires on the CPU die itself, no additional components on the package so no increased cost.
