Research Bits: August 15

Using noise for spintronics

Researchers from the Institute for Basic Science built a vertical magnetic tunneling junction device by sandwiching a few layers of vanadium in tungsten diselenide (V-WSe2), a magnetic material, between top and bottom graphene electrodes to create high-amplitude Random Telegraph Noise (RTN) signals.

Through the resistance measurement experiments using these devices, the researchers observed RTNs with a high amplitude of up to 80% between well-defined two-stable states. In the bistable state, the magnetic fluctuations in resistance prevail with temperature through the competition between intralayer and interlayer coupling among the magnetic domains. They were able to identify this bistable magnetic state through discrete Gaussian peaks in the RTN histogram with distinctive features in the noise power spectrum.

The researchers also discovered the ability to switch the bistable magnetic state and the cut-off frequency of the RTN simply by changing the voltage polarity, paving the way for the application of 1/f² noise spectroscopy in magnetic semiconductors and offers magnetic switching capability in spintronics.

“This is a first step to observe the bistable magnetic state from large resistance fluctuations in magnetic semiconductors and offers the magnetic switching capability with 1/f² noises by means of simple voltage polarity in spintronics,” said Lee Young Hee, a professor at the Center for Integrated Nanostructure Physics within the Institute for Basic Science.

Nguyen, LA.T., Jiang, J., Nguyen, T.D. et al. Electrically tunable magnetic fluctuations in multilayered vanadium-doped tungsten diselenide. Nat Electron (2023). https://doi.org/10.1038/s41928-023-01002-1

High-temperature AlN devices

Researchers from the University of Tsukuba and Dowa Electronics Materials developed Schottky-barrier diodes and metal-semiconductor field-effect transistors (MESFETs) made from aluminum nitride (AlN) that can operate stably at 827°C (1,520.6°F) and 727°C (1,340.6°F), respectively.

The AlN layers were grown on large, low-cost sapphire substrates using metal-organic chemical-vapor deposition (MOCVD), making them practically feasible to fabricate with controllable p- and n-type doping.

The wide bandgap material could be used for electronics in high-temperature applications such as underground resource drilling, space exploration, and automotive and aviation engines.

Temperature dependence of electrical characteristics of Si-implanted AlN layers on sapphire substrates, Hironori Okumura et al 2023 Appl. Phys. Express 16 064005 https://iopscience.iop.org/article/10.35848/1882-0786/acdcde

Solar power from space

Caltech researchers launched a space solar power prototype into orbit in January and has since demonstrated its ability to wirelessly transmit power in space and to beam detectable power to Earth.

The Microwave Array for Power-transfer Low-orbit Experiment (MAPLE) consists of an array of flexible lightweight microwave power transmitters driven by custom chips that were built using low-cost silicon technologies. It uses the array of transmitters to beam the energy to desired locations.

“Through the experiments we have run so far, we received confirmation that MAPLE can transmit power successfully to receivers in space,” said Ali Hajimiri, professor of electrical engineering and medical engineering at Caltech. “We have also been able to program the array to direct its energy toward Earth, which we detected here at Caltech. We had, of course, tested it on Earth, but now we know that it can survive the trip to space and operate there.”

Using constructive and destructive interference between individual transmitters, a bank of power transmitters is able to shift the focus and direction of the energy it beams out, without any moving parts. The transmitter array uses precise timing-control elements to dynamically focus the power selectively on the desired location using the coherent addition of electromagnetic waves.

MAPLE features two separate receiver arrays located about a foot away from the transmitter to receive the energy, convert it to DC, and use it to light up a pair of LEDs to demonstrate the full sequence of wireless energy transmission at a distance in space. MAPLE tested this in space by lighting up each LED individually and shifting back and forth between them. The experiment is not sealed, so it is subject to the harsh environment of space, including the wide temperature swings and solar radiation that will be faced one day by large-scale space solar power units.