Chameleon-like material mixed with boron comes closer to mimicking brain cells

Every waking moment, our brain processes a huge amount of data in order to understand the outside world. By mimicking the way the human brain solves everyday problems, neuromorphic systems have enormous potential to revolutionize big data analysis and pattern recognition problems that are a battle for current digital technologies. For artificial systems to be more brain-like, however, they have to simulate the communication between nerve cells at their terminals, the so-called synapses.

In one in the September issue of the Journal of the American Chemical SocietyResearchers at Texas A&M University have described a new material that detects the pattern of electrical activity at the synapse. Similar to how a nerve cell generates a pulse of the oscillating current depending on the history of electrical activity at its synapse, the researchers oscillate from the metal to the insulator at a transition temperature that is determined by the device’s thermal history.

Materials are generally classified into metals or insulators, depending on whether they conduct heat and electricity. However, some materials such as vanadium dioxide double the life. At certain temperatures, vanadium dioxide acts like an insulator and resists the flow of heat and electrical currents. However, when vanadium dioxide is heated to 67 degrees Celsius, it changes its internal properties in a chameleon-like manner and turns into a metal.

These reciprocating vibrations due to temperature make vanadium dioxide an ideal candidate for brain-inspired electronic systems because neurons also generate a vibrational current known as an action potential.

By adding small amounts of the element boron to vanadium dioxide, the material works like a synapse. Photo credit: Texas A&M Engineering

Neurons also bundle their inputs at their synapse. This integration steadily increases the tension of the neuron’s membrane, bringing it closer to a threshold value. When this threshold is exceeded, neurons fire an action potential.

“A neuron can remember what tension its membrane is on, and depending on where its membrane tension is in relation to the threshold, the neuron will either fire or remain inactive,” said Dr. Sarbajit Banerjee, Professor in the Department of Material Sciences and Engineering and the Department of Chemistry and one of the study’s lead authors. “We wanted to optimize the property of vanadium dioxide so that it reminds a little of how close it is to the transition temperature so that we can start mimicking what is happening at the synapse of biological neurons.”

The transition temperatures for a given material are generally fixed, unless an impurity called a dopant is added. Although a dopant can move the transition temperature within vanadium dioxide depending on its type and concentration, it was the goal of Banerjee and his team to increase or decrease the transition temperature so that not only the concentration of the dopant but also the time has passed since it was reset. That flexibility was only possible when they used the boron.

When the researchers added boron to vanadium dioxide, the material still switched from an insulator to a metal, but the transition temperature now depended on how long it stayed in a new metastable state created by boron.

“Biological neurons have a memory for their membrane tension. Similarly, boron-added vanadium dioxide has a memory for its thermal history or, formally, how long it has been in a metastable state,” said Dr. Diane Sellers, one of the study’s primary authors and a former researcher at Banerjee’s laboratory. “This memory determines the transition temperature at which the device is driven to oscillate from metal to an insulator.”

While their system is a first step towards mimicking a biological synapse, experiments are currently being conducted to make the material’s behavior more dynamic by controlling the kinetics of the relaxation process of vanadium dioxide, said Dr. Patrick Shamberger, professor in the Department of Materials Science and a corresponding author of the study.

In the near future, Dr. Xiaofeng Qiang, professor in the Department of Materials Science and a contributor to Banerjee on this project, to expand current research by studying the atomic and electronic structures of other more complex vanadium oxide compounds. In addition, the collaborative team will investigate the possibility of making other neuromorphic materials with alternative dopants.

“We want to investigate whether the phenomenon we observed with vanadium dioxide applies to other host lattices and other guest atoms,” said Dr. Raymundo Arróyave, professor in the Department of Materials Science and corresponding author of the study. “This finding can offer us different tools to further optimize the properties of these types of neuromorphic materials for different applications.”

Erick J. Braham from the Department of Chemistry is co-author of this study. Other contributors to this research include Baiyu Zhang, Drs. Timothy D. Brown, and Heidi Clarke from the Department of Materials Science; Ruben Villarreal of the J. Mike Walker ’66 Department of Mechanical Engineering; Abhishek Parija, Theodore EG Alivio and Dr. Luis R. De Jesus from the Department of Chemistry; Dr. Lucia Zuin from the University of Saskatchewan, Canada; and Dr. David Prendergast of the Lawrence Berkeley National Laboratory, California.

Researchers are making advances in controlling chameleon-like material for next-generation computers

More information:
Diane G. Sellers, et al. Atomic hourglass and thermometer based on the diffusion of a mobile dopant in VO2, Journal of the American Chemical Society (2020). DOI: 10.1021 / jacs.0c07152

Provided by the Texas A&M University College of Engineering

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