The University of Minnesota has sputtered a ‘topological insulator’ – a solid that conducts on its surface but not inside – avoiding the single crystal growth process or molecular beam epitaxy normally needed.

Bismuth selenide (Bi2Se3) is the material, magnetron-sputtered into a thin film of particles <6nm across in hetero-structures with CoFeB –

“Using the sputtering process to fabricate a quantum material like a bismuth-selenide-based topological insulator is against the intuitive instincts of all researchers in the field and actually is not supported by any existing theory,” said engineering professor Jian-Ping Wang.

As grain size was decreased, quantum confinement emerged – where electrons in the material act differently than in bulk, giving additional control over the electron behaviour.

Such materials could exploit spin–orbit torque to create fast low-power memory.

In this case, the material BixSe(1–x)/Co20Fe60B20 delivered a spin torque efficiency of over 18, “moreover, switching of the perpendicular CoFeB multilayers using the spin-orbital torque from the BixSe(1–x) was observed at room temperature with a low critical magnetisation switching current density of 4.3×105A/cm2,” said the team in the abstract of ‘Room-temperature high spin–orbit torque due to quantum confinement in sputtered BixSe(1–x) films‘, published in Nature Materials.

“We used a quantum material that has attracted a lot of attention by the semiconductor industry in the past few years, but created it in unique way that resulted in a material with new physical and spin-electronic properties that could greatly improve computing and memory efficiency,” said Wang.

The University of Minnesota worked with Semiconductor Research Corporation and the US Defense Advanced Research Projects Agency.

By: DocMemory
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