New Type of Transistor One Step Closer
October 18, 2019 | University of GroningenEstimated reading time: 2 minutes
In order to make transistors that operate using the spin of electrons, rather than their charge, it is necessary to find a way of switching spin currents on and off. Furthermore, the lifetime of the spins should at least be equal to the time taken for these electrons to travel through a circuit. University of Groningen scientists have now taken an important step forward by creating a device that meets both of these requirements, based on a double layer of graphene on top of a layer of tungsten disulfide. Their results have been published on 16 October in the journal Physical Review B.
Graphene, a two-dimensional form of carbon, is an excellent conductor of electron spins. However, it is difficult to manipulate spin currents in this material. Spin is a quantum mechanical property of electrons, which makes them behave like tiny magnets. The Physics of Nanodevices group at the University of Groningen, led by Professor Bart van Wees, is working on this problem. They have previously shown that it is possible to control spin currents if the graphene is placed on top of a layer of tungsten disulphide (another 2D material).
New Technique
"However, this approach reduces the lifetime of the spins," explains Siddhartha Omar, a postdoc in the Van Wees group. Tungsten is a metal, and its atoms influence the electrons passing through the graphene, dissipating the spin currents. This led Omar to use a double layer of graphene on the tungsten disulphide, based on the theory that electrons passing through the upper layer should 'feel' less of the metal atoms' influence.
Omar also used another new technique, in which two different types of spin current are passed through the graphene. Spin is a magnetic moment that has a given direction. In normal materials, the spins are not aligned. However, the magnetic moment of spin currents—like that of magnets—has a preferential alignment. Relative to the material through which the electrons are passing, their spins can either have an in-plane orientation or an out-of-plane orientation.
Energy Level
"We found that, as the electrons pass through the outer graphene layer, the in-plane spins are dissipated very quickly—in mere picoseconds. However, the lifetime of the out-of-plane spins is about one hundred times longer." This means that, even in the presence of tungsten disulphide, one component of spin currents (spins with an out-of-plane orientation) can travel far enough to be used in devices such as transistors.
The energy level of the spin currents observed by Omar caused them to pass through the upper layer of graphene. This energy level can be boosted by applying an electric field, pushing the spin currents into the lower layer. "Down there, the spins will feel the full effect of the metal atoms and the spin currents will quickly dissipate," Omar explains. This ability to switch the spin current off using an electric field is important, as it could be used to 'gate' transistors based on this technology.
"Unfortunately, certain technical limitations of the substrate on which we built these devices prevent us from creating electric fields that are strong enough to produce this gating effect," says Omar. "However, we have shown that it is possible to send spin currents through a heterostructure made of graphene and tungsten disulphide. That is an important step towards the creation of a spin transistor."
Suggested Items
Kioxia, WD Elevate Capacity Utilization, Pushing NAND Flash Supply Growth to 10.9%
03/19/2024 | TrendForceTrendForce reports that anticipation of NAND Flash price hikes into Q2 has motivated certain suppliers to minimize losses and lower costs in hopes of returning to profitability this year.
Izumo Murata to Start Construction of New Production Building
02/05/2024 | MurataIzumo Murata Manufacturing Co., Ltd., a manufacturing subsidiary of Murata Manufacturing Co., Ltd., located in Izumo City, Shimane Prefecture, will start constructing a new production building in March 2024.
Lockheed Martin Awarded Contract For 18 Space Development Agency Tranche 2 Satellites
01/18/2024 | Lockheed MartinThe Space Development Agency (SDA) has awarded Lockheed Martin (NYSE: LMT) a contract to build 18 space vehicles as part of its Tranche 2 Tracking Layer constellation.
Space Development Agency Awards L3Harris $919 Million Contract to Build Satellites for Missile Tracking Program
01/17/2024 | BUSINESS WIREL3Harris Technologies received a contract with a potential value of up to $919 million to design and build 18 infrared space vehicles for the Space Development Agency’s (SDA) Tranche 2 (T2) Tracking Layer program that will provide near-global missile warning and tracking coverage.
Connect the Dots: Five Best Practices for Designing Flex and Rigid-flex PCBs
01/09/2024 | Matt Stevenson -- Column: Connect the DotsFlex and rigid-flex PCBs represent exciting technology for designers. Suddenly, boards no longer need to exist along one plane—or along a flat plane at all. Designs can now conform to specific shapes or be bent during use, opening new possibilities for applications with space constraints or flexibility requirements.