On-chip inductors get smaller with graphene and electron momentum

US researchers have made on-chip inductors smaller by adding ‘kinetic inductance’ to conventional magnetic inductance.


The work cuts the size of 10-50GHz inductors by a third.

Kinetic inductance arises from the physical momentum of charge carriers resisting the change in current direction associated with a change in electric field, according to the team, from the University of California, Santa Barbara.

Any kinetic inductance created appears in series with the conventional magnetic inductance of the inductor.

However, the metals almost universally used in inductors exhibit only negligible kinetic inductance.

“The theory of kinetic inductance has long been known in condensed-matter physics, but nobody ever used it for inductors, because in conventional metallic conductors, kinetic inductance is negligible,” said project leader Professor Kaustav Banerjee.

So the team created a material with significant built-in kinetic inductance: using multi-layer graphene with bromine atoms between the layers – ‘intercalated with bromine atoms’.

“Single-layer graphene exhibits a linear electronic band structure and a correspondingly large momentum relaxation time [MRT] – a few picoseconds,” said the University. “This is higher compared to that of conventional metallic conductors like copper, which ranges from 1-10fs. But single-layer graphene has too much resistance for application on an inductor.”

Multi-layer graphene offers a partial solution by providing lower resistance, but due to inter-layer couplings, the MRT is not good enough.

Chemically inserting bromine atoms between the graphene layers, according  to the University, separates layers enough to decouple them somewhat, increasing kinetic inductance by extending MRT, and it further reduced resistance as a bonus.

This was then made into a spiral inductor.

“There is plenty of room to increase the inductance density further by increasing the efficiency of the intercalation process, which we are now exploring,” said scientist Junkai Jiang.

The work is published as ‘On-chip intercalated-graphene inductors for next-generation radio frequency electronics‘ in Nature Electronics


The Nanoelectronics Research Lab of UCSB worked with the Shibaura Institute of Technology in Japan and Shanghai Jiao Tong University in China.

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