Here’s what I think is happening:
Copper exhibits what is called ‘skin effect’ at high frequencies, where the primary conduction of the signal is along the outer layer of the conductor.
The Graphene is coating the outer layer of the copper so it enhances the conduction of the copper wire’s skin effect, by Ohm’s Law, where two conductors in parallel will have a lower resistance that either one of them singularly.
This would in effect be electrically shortening the paths so the signals could be of higher frequency than with copper coated with tantalum nitride ..............
I expect that you are on the right track Red Badger. The solid state physicists at FR are probably too busy designing to weigh in, but there are likely many issues at work, and probably being considered by semiconductor designers before this Graphene layer can become deployed. My guess, given that the performance number given is about 30%, that this is another design rules shrink. Shrinking design rules are constrained by interconnect limitations. The “wires” inside a processor with over 1 1/2 billion transistors, and probably double that number of simple gates, is enormous, probably over 40 billion. The delay through the wires connecting all those devices limits frequencies, since 64 bit registers must have 64 bits all loaded before those registers can be read. When data arrive irregularly it is called “skew”. I’m guessing that Graphene is more important for its thinness and to minimize contamination, since the silicon substrate is an insulator unless it is “contaminated”, accidentally, or intentionally, as in “doped”, the process used to create semiconductors.
Perhaps we have an expert who can correct me or illuminate the issue? Few understand what a wonder our semiconductors are. To add what little else I have encountered measuring electrical signals, the dielectric constant of the insulator has a significant effect upon the velocity of electrical signals through a conductor. We used to estimate electrical pulse velocity at 7 inches/nanoseconds or about 60% of the velocity of light in a vacuum. Today’s semiconductors behave like waveguides, only they are built of millions of waveguides, yes, radio frequencies. These waveguides behave just like those pipes inside radar transmitters and receivers, but carry much less power. If they didn’t, a 4 Gigahertz processor couldn’t work since there would be no way to pass bits between logical units, or even to differentiate ones from zeros.