It is not alive and has no structures even approaching the complexity of the brain, but a compound called vanadium dioxide is capable of “remembering” previous external stimuli, researchers have found.
This is the first time this ability has been identified in material; but it may not be the last. The discovery has some rather intriguing implications for the development of electronic devices, particularly data processing and storage.
“Here we report electronically accessible long-lived structural states in vanadium dioxide that can provide a scheme for data storage and processing,” a team of researchers led by electrical engineer Mohammad Samizade Nico of the École Polytechnique Fédérale de Lausanne in Switzerland wrote in their paper.
“These glass-like functional devices could surpass conventional metal-oxide-semiconductor electronics in terms of speed, power consumption, and miniaturization, as well as provide a path to neuromorphic computing and multilevel memories.”
Vanadium dioxide (VO2) is a material that has recently been proposed as an alternative or complement to silicon as a basis for electronic devices due to its potential to outperform the latter material as a semiconductor.
One of the most intriguing properties of VO2 is that below 68 degrees Celsius (154.4 degrees Fahrenheit) it behaves like an insulator – but above this critical temperature it suddenly changes to a highly conductive metal, a change known as the metal-insulator transition.
Only recently, in 2018, did scientists discover why: as temperature rises, the way atoms arrange themselves in their lattice changes.
When the temperature drops back down, the material returns to its original state of insulation. Samizadeh Nikoo initially set out to investigate how long VO is2 it goes from insulator to metal and back, making measurements as it actuates the switch.
It was these measurements that revealed something very strange. Although it returned to the same starting state, VO2 acted as if remembered Recent activity.
The experiments involved introducing an electric current to the material, which followed a precise path from one side to the other. This current heated the VO2, causing it to change its state – the aforementioned rearrangement of the atomic structure. When the current was removed, the atomic structure relaxed again.
When the current was applied again, things got interesting.
“VO2 they seem to ‘remember’ the first phase transition and expect the next one,” explains electrical engineer Alison Mattioli from EPFL. “We didn’t expect to see this kind of memory effect, and it has nothing to do with electronic states, but rather with the physical structure of the material. This is a new discovery: no other material behaves in this way.”
The team’s work revealed that VO2 stores some information about the last applied current for at least three hours. In fact, it could be significantly longer—”but we don’t currently have the tools to measure that,” Mattioli says.
The switch resembles the behavior of neurons in the brain, which serve as both a memory unit and a processor. Described as neuromorphic technology, computing based on such a system could have a real advantage over classic chips and boards.
Since this dual property is innate to the material, VO2 seems to tick all the boxes on the memory device wish list: high capacity potential, high speed and scalability. In addition, its properties give it an advantage over memory devices that encode data in a binary format controlled by electrical states.
“We reported glassy dynamics in VO2 that can be excited on subnanosecond time scales and observed over several orders of magnitude, from microseconds to hours,” the researchers wrote.
“In this way, our functional devices can potentially meet the continuous demands of electronics in terms of downscaling, fast operation and power level reduction.”
The study was published in Natural electronics.