Chameleon-like material enriched with boron is closer to mimicking brain cells

Every moment we wake up, our brain processes an enormous amount of data to make sense of the outside world. By imitating the way the human brain solves everyday problems, neuromorphic systems have tremendous potential to revolutionize big data analysis and pattern recognition problems that are a struggle for current digital technologies. But for artificial systems to be more brain-like, they have to replicate how nerve cells communicate at their terminals, called the synapses.

In a study published in the September issue of the Journal of the American Chemical Societyresearchers at Texas A&M University described a new material that records the pattern of electrical activity at the synapse. Just as a nerve cell produces a pulse of oscillating current depending on the history of electrical activity at its synapse, the researchers said their material oscillates from metal to insulator at a transition temperature determined by the device’s thermal history.

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

These back-and-forth oscillations due to temperature make vanadium dioxide an ideal candidate for brain-inspired electronic systems, as neurons also produce an oscillating current called an action potential.

But neurons also bundle their input in their synapse. This integration steadily increases the tension of the neuron membrane, bringing it closer to a threshold. When this threshold is exceeded, neurons fire an action potential.

“A neuron can remember what voltage its membrane is on and depending on where its membrane voltage is relative to the threshold, the neuron will either fire or remain inactive,” said Dr. Sarbajit Banerjee, professor in the Department of Materials Science and Engineering. and the Department of Chemistry, and one of the study’s senior authors. “We wanted to adjust the property of vanadium dioxide so that it retains a memory of how close it is to the transition temperature, so we can begin to mimic what is happening in the synapse of biological neurons. ”

The transition temperatures for a particular material are generally fixed unless an impurity called a dopant is added. While a dopant can change the transition temperature depending on its type and concentration in vanadium dioxide, Banerjee and his team set out to create a way to raise or lower the transition temperature in a way that would not only reduce the concentration of the dopant, as well as the elapsed time since it was reset. This flexibility, they discovered, was only possible if they used the drill.

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

“Biological neurons have a memory of their membrane tension; similarly, boron vanadium dioxide has a memory of its thermal history, or formally speaking, how long it has been in a metastable state,” said Dr. Diane Sellers, one of the study’s main authors and a former researcher in Banerjee’s lab. “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 in mimicking a biological synapse, experiments are currently underway to introduce more dynamics into the behavior of the material by controlling the kinetics of the vanadium dioxide relaxation process, 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 Banerjee collaborator on this project, plans to expand current research by examining the atomic and electronic structures of other more complex vanadium oxide compounds. In addition, the collaboration team will also explore the possibility of creating other neuromorphic materials with alternative dopants.

“We would like to investigate whether the phenomenon we observed with vanadium dioxide also applies to other gas lattices and other gas atoms,” says Dr. Raymundo Arróyave, professor in the department of materials science and a corresponding author on the study. “This insight can provide us with various tools to further fine-tune the properties of these types of neuromorphic materials for various applications.”

Erick J. Braham from the Department of Chemistry is a co-primary author of this study. Other contributors to this study include Baiyu Zhang, Drs. Timothy D. Brown and Heidi Clarke from the Materials Science Department; Ruben Villarreal from J. Mike Walker’s Mechanical Engineering Department ’66; 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 Lawrence Berkeley National Laboratory, California.