It is not living, or even close to the complexity of the brain, but researchers have found that a compound called vanadium dioxide can “remember” previous external stimuli.
This is the first time this ability has been found in the material, but this may not be the last time. This finding has an intriguing impact on the development of electronic devices, particularly data processing and storage.
A team led by Mohammad Samizadeh Nikoo, an electrical engineer at the Federal Institute of Technology in Lausanne, Switzerland, wrote in their paper: “Here, we report the long-life structural state available for electrons in vanadium dioxide, which can provide a solution for data storage and processing.”
These glass-like functional devices may surpass traditional metal oxide semiconductor electronics in terms of speed, energy consumption, and miniaturization, and provide a route to neuromorphic computing and multilevel memory.
Vanadium dioxide (VO2) is a recently surfaced material that replaces or supplements silicon as the basis for electronic devices because it has the potential to surpass the latter as a new semiconductor material.
One of the most interesting properties of VO2 is that below 68 degrees Celsius (154.4 degrees Fahrenheit) it behaves as an insulator, but above this critical temperature it suddenly transforms into a metal with good conductivity, a change known as the “metal-insulator transition”.
Only recently, 2018, scientists discovered the reason: as temperatures rise, the arrangement of atoms in lattice patterns changes.
When the temperature drops, the material returns to its original insulator state. Mohammed Samizad Niku initially intended to investigate how long it took for VO2 to transition from insulator to metal, and vice versa. He measured when he triggered the switch.
It is these measurements that reveal something very strange. Although, it returns to the same starting state, VO2 behaves just as it remembers recent activity.
The experiment involves introducing a current into the material so that it passes from one end to the other in a precise path. This current heats VO2, causing it to change the state (rearrangement of the atomic structure mentioned earlier). When the current is removed, the atomic structure relaxes again.
When the current is reinjected, things become interesting.
Elison Matioli, an electrical engineer at EPFL, explained: “VO2 seems to ‘remember’ the first phase transition and predict the next. We did not think of seeing this memory effect, which is not related to the electronic state, but to the physical structure of the material. This is a new finding: no other material has this property.”
The team’s work revealed that VO2 stored some kind of information for at least three hours on the nearest applied current. In fact, it may grow much longer. “But we don’t currently have the instruments to measure it,” says Ellison Mattheoli.
This conversion is reminiscent of the behavior of neurons in the brain, which are both storage units and processors. Known as neuromorphic technology, calculations based on similar systems may have real advantages over traditional chips and circuit boards.
Because this dual property of this material is innate, VO2 seems to fulfill all the requirements of memory devices: with the potential for high capacity, high speed, and scalability. In addition, its characteristics make it advantageous on storage devices encoding data in binary format controlled by electronic states.
“We have reported glassy dynamics in VO2 that can excite on a sub-nanosecond timescale and monitor over several orders of magnitude, from microseconds to hours,” the researchers write. “Therefore, our functional devices meet the continued demand of electronics for scale-down, fast operation, and reduced voltage supply levels.”