In recent years, graphene has been intensively studied for interconnect applications, where it has potential to fulfill diverse roles.
The material has for example been considered as an oxidation barrier and as an ultrathin diffusion barrier for metals.
Researchers have also investigated the feasibility of using multilayer graphene wires or nanoribbons as an alternative conductor.
Despite these interesting properties, graphene has one major drawback: intrinsically, it does not hold enough charge carriers to be useful as a local interconnect.
The lack of charge carriers severely reduces its electrical conductivity, a key metric for interconnect performance that is proportional to both the mobility and the carrier concentration.
Fortunately, there are ways to further modulate graphene’s conductivity.
This has driven the research of so-called graphene nanoribbons – graphene layers patterned into narrow strips.
The specific angular orientation of the graphene layers with respect to their underlying layer provides another knob for improvement.
Finally, the conductivity of graphene can be boosted by doping, this way providing graphene with extra electrons or holes to carry the current.
Doping can be performed in several ways, for example by metal-induced doping – enabled by bringing graphene in direct contact with metals like Cu or Ru.
These hybrid metal/graphene schemes bring together the best of both ‘worlds’: the high carrier concentration of the metal and the high mobility of graphene.
Graphene-capped metal hybrid structures provide an answer to the RC delay problem for future interconnects.
While graphene-capped metal interconnects are the most mature, stacks of alternating layers may come into play in the longer term.
