Researchers use graphene and other 2D materials to create a spin field-effect transistor at room temperature

Researchers at CIC nanoGUNE BRTA in Spain and University of Regensburg in Germany have recently demonstrated spin precession at room temperature in the absence of a magnetic field in bilayer graphene. In their paper, the team used 2D materials to realize a spin field-effect transistor.

Sketch of a graphene-WSe2 spin field-effect transistor imageSketch of the spin field-effect transistor. Image from article

Coherently manipulating electron spins at room temperature using electrical current is a major goal in spintronics research. This is particularly valuable as it would enable the development of numerous devices, including spin field-effect transistors. In experiments using conventional materials, engineers and physicists have so far only observed coherent spin precession in the ballistic regime and at very low temperatures. Two-dimensional (2D materials), however, have unique characteristics that could provide new control knobs to manipulate spin procession.

Gate-controlled magnetic phase transition in a van der Waals magnet

An international collaboration led by RMIT has achieved record-high electron doping in a layered ferromagnet, causing magnetic phase transition with significant promise for future electronics.

Control of magnetism (or spin directions) by electric voltage is vital for developing future, low-energy high-speed nano-electronic and spintronic devices, such as spin-orbit torque devices and spin field-effect transistors. Ultra-high-charge, doping-induced magnetic phase transition in a layered ferromagnet allows promising applications in antiferromagnetic spintronic devices.

Researchers map the electronic spins in a working MOS2 transistor

An international research team, led by the University of Tsukuba, has used electron spin resonance (ESR) to monitor the number and location of unpaired spins going through a molybdenum disulfide transistor. ESR uses the same physical principle as the MRI machines that create medical images. The spins are subject to a very strong magnetic field, which creates an energy difference between electrons with spins aligned and anti-aligned with the field. The absorbance of photons that match this energy gap can be measured to determine the presence of unpaired electron spins.

Schematic diagram of the MoS2 transistor in an ESR sample tube image15 1 Share Email Home Physics Condensed Matter MARCH 5, 2021 Taking 2-D materials for a spin by University of Tsukuba Schematic diagram of the MoS2 transistor in an ESR sample tube. Credit: University of Tsukuba

The experiment required the sample to be cooled to just four degrees above absolute zero, and the transistor to be in operation while the spins are being measured. "The ESR signals were measured simultaneously with the drain and gate currents," corresponding author Professor Kazuhiro Marumoto says. "Theoretical calculations further identified the origins of the spins," coauthor Professor Małgorzata Wierzbowska says. Molybdenum disulfide was used because its atoms naturally form a nearly flat two-dimensional structure. The molybdenum atoms form a plane with a layer of sulfide ions above and below.

Rice researchers develop theory that could push spintronics forward

A new theory by Rice University scientists could boost the field of spintronics. Materials theorist Boris Yakobson and graduate student Sunny Gupta at Rice’s Brown School of Engineering describe the mechanism behind Rashba splitting, an effect seen in crystal compounds that can influence their electrons’ “up” or “down” spin states, analogous to “on” or “off” in common transistors.

Theory could accelerate push for spintronic devices imageThe left shows the crystal structure of a MoTe2

The Rice model characterizes single layers to predict heteropairs — two-dimensional bilayers — that enable large Rashba splitting. These would make it possible to control the spin of enough electrons to make room-temperature spin transistors, a far more advanced version of common transistors that rely on electric current.

Researchers create a graphene-based 2D spin transistor

Researchers from the University of Groningen developed a two-dimensional spin transistor, in which spin currents were generated by an electric current through graphene. The device also include a monolayer transition metal dichalcogenide (TMD) that is placed on the graphene to induce charge-to-spin conversion.

Scientists create fully electronic 2-dimensional spin transistors image

Graphene is an excellent spin transporter, but spin-orbit coupling is required to create or manipulate spins. The interaction is weak in the graphene carbon atoms, but now the researchers have shown that adding the TMD layer increases the spin-orbit coupling.

US researchers designed an efficient graphene-based spintronics transistor

Researchers from the University of Nebraska-Lincoln designed a spintronics transistor that is based on graphene. The researchers say that such a device could be highly efficient, run at room temperature (and above) and feature a nonvolatile on-off current ratio and electrically controllable spin polarization.

Top-gated graphene-based magnetoelectric spinFET design

The device is based on the discovery that an external voltage can be used to control the magnetic properties of few-layer graphene interfaced with chromium oxide. This is a theoretical research at this stage but the new device structure is expected to feature a large electrically controllable spin current.

Intel: we'll have to adopt fundamentally new transistor technologies in 4-5 years, Spintronics is a leading candidate

Intel's technology and manufacturing group leader, William Holt, says that if Intel wants to keep improving its chips, it will soon have to start using fundamentally new technologies. The company does not know which technology will be adopted, but there are two possible candidates at this stage - Spintronics, and tunneling transistors.

William says that the new technologies will have to be commercialized in four to five years (when Intel moves over to 7-nm production, which is thought to be the limit of silicon transistors), and will initially be used alongside silicon transistors. Intel says we'll need to stop expecting chips to be faster - as the new technologies will mostly benefit the energy efficiency rather than the speed of Intel's future chips.

Graphene can filter electrons according to the direction of their spin

Researchers from MIT discovered that under a powerful magnetic field and at very low temperatures, graphene can filter electrons according to the direction of their spin. This is something that cannot be done by any conventional electronic system - and may make graphene very useful for quantum computing.

it is known that when a magnetic field is turned on perpendicular to a graphene flake, current flows only along the edge, and in one direction (clockwise or counterclockwise, depending on the magnetic field orientation), while the bulk graphene sheet remains insulating. This is called the Quantum Hall effect.

The world's first 3D Spintronics chip developed at Cambridge

Researchers from the University of Cambridge in the UK have developed the world's first 3D microchip, based on Spintronics technology. The chip basically uses atoms to store and transfer the data - and not electronic transistors. This may lead to 3D MRAM chips that have a large memory density - thousands of times larger than what's available today.

To create this chip they used sputtering - effectively making a sandwich on a silicon chip of cobalt, platinum and ruthenium atoms. The cobalt and platinum atoms store the digital information in a similar way to how a hard disk drive stores data. The ruthenium atoms act as messengers, communicating that information between neighboring layers of cobalt and platinum. Each of the layers is only a few atoms thick.

Electron spin-splitting (Rashba effect) shown in Bismuth selenide

Electron spin-splitting effect (Rashba effect) was demonstrated in a semiconductor (Bismuth selenide) that is far larger than has ever been seen before. This could lead the way towards room-temperature spintronic devices. The Rashba effect is the phenomenon of spin splitting with an applied electric field instead of a magnetic field.

The Rashba effect is crucial for spintronic devices: for example when designing spin transistors, electrons of a single spin are injected and then – under an applied electric field – have their spins rotated. Rashba effect in well-established semiconductors (silicon or gallium arsenide for example) is very small - and so electrons have to travel large distances before any spin rotation is noticeable. This requires very pure materials and very low temperatures.