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Content archived on 2024-05-28

Spin Transport in Silicon Nanodevices

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Silicon spintronics extends the range of present semiconductor technology

The era of the silicon-based complementary metal-oxide semiconductor is nearing a point where further scaling will be difficult and there will be no room for further improvements in thermal dissipation and device performance. An EU-funded project harnessed silicon – the workhorse of the semiconductor and electronics industry – and other semiconductor materials for spintronics applications that can change the paradigm in how to approach scaling.

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Modern electronic devices operate because negatively charged electrons flow as electrical current. While in current transistors the presence or absence of current flowing is represented by 1 or 0 correspondingly, in spintronic devices 1 and 0 are represented by an up or down spin. In addition to electrical charge, spintronics use the intrinsic spin property of electrons for higher data transfer speeds and increased storage capacity. Silicon, graphene, germanium and topological insulators have proved promising materials for spintronics applications owing to their capacity for room-temperature spin transport over long diffusion lengths. These materials can retain their electron spin state (orientation) for several micrometres, which is important for quantum information storage and computing. The EU-funded project SILICONSPIN (Spin transport in silicon nanodevices) shed new insight into the fundamental physical principles of spin generation, manipulation and transport in these materials and across tunnel barriers. Researchers employed different sophisticated techniques for creating spin polarisation in silicon and germanium at room temperature. Use of ferromagnetic electrodes for detecting the spin introduced big leaps in tunnel magnetoresistance, increase in spin lifetimes and spin accumulation. Using a 2D insulating hexagonal boron nitride (h-BN) as a tunnel barrier in the magnetic tunnel junction, the team injected spin-polarised current from a ferromagnetic electrode into silicon. This generated currents flowing both in the same and opposite directions. In addition to relying on ferromagnetic electrodes for injecting spin polarisation in silicon, researchers also employed thermal heating of silicon and dynamical methods. Using these methods, they reported for the first time spin accumulation and spin pumping in silicon. Another SILICONSPIN focus was on exploring spin transport on graphene at room temperature. By depositing graphene on silicon or silicon dioxide substrates, the team reported high diffusion lengths and spin lifetimes in the order of a few nanoseconds. Once again, researchers used h-BN as a tunnel barrier in the magnetic tunnel junction and reported a higher degree in spin polarisation. The use of electron spin currents to process information is viewed as the holy grail of semiconductor spintronics since it leads to devices of higher performance and lower power consumption, also eliminating heat build-up. Generating and modulating spin current in semiconductors can lead to tailor-made spintronic devices with new functionalities.

Keywords

Silicon, spintronics, semiconductor, graphene, spin transport, SILICONSPIN

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