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New Material Could Improve Efficiency Of Computer Processing And Memory

This cross-sectional transmission electron microscope image shows a sample used for the charge-to-spin conversion experiment. The nano-sized grains of less than 6 nanometers in the sputtered topological insulator layer created new physical properties for the material that changed the behavior of the electrons in the material. Credit: Wang Group, University of Minnesota

A team of researchers led by the University of Minnesota has
developed a new material that could potentially improve the efficiency of
computer processing and memory. The researchers have filed a patent on the material
with support from the Semiconductor Research Corporation, and people in the
semiconductor industry have already requested samples of the material.

The findings are published in Nature Materials, a
peer-reviewed scientific journal published by Nature Publishing Group.

"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
lead researcher Jian-Ping Wang, a University of Minnesota Distinguished
McKnight Professor and Robert F. Hartmann Chair in electrical engineering.

The new material is in a class of materials called
"topological insulators," which have been studied recently by physics and
materials research communities and the semiconductor industry because of their
unique spin-electronic transport and magnetic properties. Topological
insulators are usually created using a single crystal growth process. Another
common fabrication technique uses a process called Molecular Beam Epitaxy in
which crystals are grown in a thin film. Both of these techniques cannot be
easily scaled up for use in the semiconductor industry.

In this study, researchers started with bismuth selenide
(Bi2Se3), a compound of bismuth and selenium. They then used a thin film
deposition technique called "sputtering," which is driven by the momentum
exchange between the ions and atoms in the target materials due to collisions.
While the sputtering technique is common in the semiconductor industry, this is
the first time it has been used to create a topological insulator material that
could be scaled up for semiconductor and magnetic industry applications.

However, the fact that the sputtering technique worked was
not the most surprising part of the experiment. The nano-sized grains of less
than 6 nanometers in the sputtered topological insulator layer created new
physical properties for the material that changed the behavior of the electrons
in the material. After testing the new material, the researchers found it to be
18 times more efficient in computing processing and memory compared to current

"As the size of the grains decreased, we experienced what we
call "˜quantum confinement' in which the electrons in the material act
differently giving us more control over the electron behavior," said study
co-author Tony Low, a University of Minnesota assistant professor of electrical
and computer engineering.

Researchers studied the material using the University of
Minnesota's unique high-resolution transmission electron microscopy (TEM), a
microscopy technique in which a beam of electrons is transmitted through a
specimen to form an image.

"Using our advanced aberration-corrected scanning TEM we
managed to identify those nano-sized grains and their interfaces in the film,"
said Andre Mkhoyan, a University of Minnesota associate professor of chemical
engineering and materials science and electron microscopy expert.

Researchers say this is only the beginning and that this
discovery could open the door to more advances in the semiconductor industry as
well as related industries, such as magnetic random access memory (MRAM)

"With the new physics of these materials could come many new
applications," said Mahendra DC (Dangi Chhetri), first author of the paper and
a physics Ph.D. student in Professor Wang's lab.

Wang agrees that this cutting-edge research could make a big

"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," Wang said. "Four years ago, with a strong
support from Semiconductor Research Corporation and the Defense Advanced
Research Projects Agency, we started with a big idea to search for a practical
pathway to grow and apply the topological insulator material for future
computing and memory devices. Our surprising experimental discovery led to a
new theory for topological insulator materials.

"Research is all about being patient and collaborating with
team members. This time there was a big pay off," Wang said.

In addition to Wang, Low, Mkhoyan, and DC, other researchers
who were part of the team included University of Minnesota post-doctoral
researchers and graduate students Mahdi Jamali, Junyang Chen, Danielle Hickey,
Delin Zhang, Zhengyang Zhao, Hongshi Li, Patrick Quarterman, Yang Lv, and associate
professor Aurelien Manchon from King Saud University, Saudi Arabia.

This research was funded by the Center for Spintronic
Materials, Interfaces and Novel Architectures (C-SPIN) at the University of
Minnesota, a Semiconductor Research Corporation program sponsored by the
Microelectronics Advanced Research Corp. (MARCO) and the Defense Advanced
Research Projects Agency (DARPA). This research used the University of
Minnesota College of Science and Engineering Characterization Facility. The
research was supported in part by the National Science Foundation through
University of Minnesota Materials Research Science and Engineering Center (No.
DMR-1420013); and the University of Minnesota College of Science and
Engineering's Minnesota Nano Center supported in part by the National Science
Foundation through the NSF through the National Nanotechnology Infrastructure
Network (NNIN).

To read the full research paper entitled "Room-temperature
high spin"“orbit torque due to quantum confinement in sputtered BixSe(1"“x)
films," visit the Nature Materials website.

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