Researchers have found that it is not alive and has no structures even approaching the complexity of the brain, but a compound called vanadium dioxide is able to “remember” previous external stimuli.
It is the first time that this ability is identified in a material; but it may not be the last. The discovery has quite intriguing implications for the development of electronic devices, particularly data processing and storage.
“Here we report long-lived electronically accessible structural states in vanadium dioxide that can provide a framework for data storage and processing,” writes a team of researchers led by electrical engineer Mohammad Samizadeh Nikoo of the ‘École Polytechnique Fédérale de Lausanne in Switzerland in his article.
“These functional glass-like devices could outperform conventional metal oxide and semiconductor electronics in terms of speed, power consumption and miniaturization, as well as provide a route to neuromorphic computing and multilevel memories.”
Vanadium dioxide (VO2) is a material that has recently been floated 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 as an insulator, but above this critical temperature, it abruptly changes to a metal, with good conductivity, a change known as metal. – Insulating transition.
Recently, in 2018, scientists discovered why: As the temperature rises, the way atoms arrange themselves in their lattice pattern changes.
When the temperature drops, the material returns to its original insulating state. Samizadeh Nikoo initially set out to investigate how long it takes VO2 to go from insulator to metal, and vice versa, by taking measurements when he flipped the switch.
It was these measurements that revealed something very peculiar. Although it returned to the same initial state, the VO2 behaved as if it remembered the recent activity.
The experiments involved introducing an electric current into the material, which made a precise path from one side to the other. This current heated the VO2, causing it to change state – the aforementioned rearrangement of atomic structure. When the current was removed, the atomic structure relaxed again.
When the current was applied again, things got interesting.
“VO2 seemed to ‘remember’ the first phase transition and anticipate the next one,” explains electrical engineer Elison Matioli from EPFL. “We didn’t expect to see this kind of memory effect, and it has nothing to do with the electronic states but rather with the physical structure of the material. It’s a new discovery: no other material behaves in this way.”
The team’s work revealed that VO2 stored some kind of information about the most recently applied current for at least three hours. In fact, it could be much longer, “but we don’t currently have the instruments to measure that,” says Matioli.
The switch recalls the behavior of neurons in a brain, which serve as both a memory unit and a processor. Described as neuromorphic technology, computing based on a similar system could have a real advantage over traditional chips and circuit boards.
Because this dual property is innate to the material, VO2 seems to tick all the boxes on the wish list for memory devices: potential for high capacity, high speed, and scalability. In addition, its properties give it an advantage in memory devices that encode data in a binary format controlled by electrical states.
“We have reported glass-like dynamics in VO2 that can be excited on sub-nanosecond time scales and controlled over several orders of magnitude in time, from microseconds to hours,” the researchers write.
“Our functional devices can therefore meet the continuous demands of electronics in terms of downscaling, fast operation and decreasing voltage supply level.”
The research has been published in Nature Electronics.