Researchers from the University of York and Roma Tre University have discovered a new route to ultra-low-power transistors using a graphene-based composite material. As transistors are squeezed into ever smaller areas within computer chips, the semiconductor industry struggles to contain overheating in devices.
Researchers believe the solution lies in composite materials built from monolayers of graphene and the transition metal dichalcogenide (TMDC). They discovered these materials could be used to achieve a fine electrical control over the electron's spin - its tiny compass needle.
The new research, published in the journal Physical Review Letters, could lead the way to much needed low-energy consumption electronics.
Lead researcher Dr Aires Ferreira, of the University of York's Department of Physics, said that they have been searching for good conductors that allow efficient electrical control over the electron's spin for many years. They found that this can be achieved with little effort when two-dimensional graphene is paired with certain semiconducting layered materials. Their calculations show that the application of small voltages across the graphene layer induces a net polarization of conduction spins.
Their predictions will attract substantial interest from the spintronics community. The flexible, atomically thin nature of the graphene-based structure is a major advantage for applications. Also, the presence of a semiconducting component opens up the possibility for integration with optical communication networks.
The electron’s spin is like a tiny, point-like magnet which can point only in two directions, up or down. In materials where a major fraction of electrons’ spins is aligned, a magnetic response is produced, which can be used to encode information.
‘Spin currents’ - built from ‘up’ and ‘down’ spins flowing in opposite directions - carry no net charge, and therefore in theory, produce no heating. The control of spin information would therefore open the path towards ultra-energy-efficient computer chips.
The team of researchers showed that when a small current is passed through the graphene layer, the electrons’ spin polarize in plane due to ‘spin-orbital’ forces brought about by the proximity to the TMDC base. They also showed that the efficiency of charge-to-spin conversion can be quite high even at room temperature.
Current-induced spin polarization in non-magnetic media was first demonstrated in 2001 in semiconductors and, more recently, in metallic hetero-interfaces. Now the researchers predict that a similar effect occurs in graphene on TMDC monolayer.
Surprisingly they found that the unique character of electronic states in graphene enable charge-to-spin conversion efficiency of up to 94 per cent. This opens up the possibility of a graphene-based composite material becoming the basis for ultra-compact and greener spin-logic devices.
This work follows insights gained from understanding fundamental laws that enabled them to envisage systems where the efficiency of charge-to-spin conversion can be optimal for technological applications. In particular, the much needed low-energy consumption electronics that will improve durability and performances of future devices. Click here to learn more.
