A team of researchers from the École Polytechnique Fédérale de Lausanne (EPFL) has discovered that vanadium dioxide (VO2) is capable of “remembering” the entire history of previous external stimuli. It was EPFL’s Power and Broadband Electronics Research Laboratory (POWERlab ) who came across this finding by chance while doing research on phase transitions in vanadium dioxide (VO2).
Vanadium dioxide marks the first material to be identified with this unusual property. No other material that we know of behaves in this way. In fact, it is not something alive nor does it have structures similar to those of a brain, not even remotely, but it is capable of “remembering” previous external stimuli , according to the authors in their study published in the journal Nature Electronics.
“Here we report electronically accessible long-lived structural states in vanadium dioxide that may provide a scheme for data storage and processing,” write the researchers led by electrical engineer Mohammad Samizadeh Nikoo of École Polytechnique Fédérale de Lausanne in Switzerland. “These functional glass-like devices could outperform conventional metal-oxide-semiconductor electronics in terms of speed, power consumption, and miniaturization, as well as provide a route to neuromorphic computing and multilevel memories.”
What does this discovery imply?
The findings could have important implications for the future of electronic devices, particularly with regard to data processing and storage. Engineers rely on memory to perform calculations of all kinds, and materials that could improve the calculation process by offering greater capacity, speed, and miniaturization are in high demand. This is where vanadium dioxide could play a crucial role in the future.
According to the study, VO2 has an insulating phase when it relaxes at room temperature and undergoes an abrupt transition from insulator to metal at 68°C, where its lattice structure changes. Under normal conditions, VO2 shows volatile characteristics. “The material returns to the insulating state immediately after removing the excitation,” they state.
In his experiments, Samizadeh Nikoo applied an electrical current to a VO2 sample. The current moved through the material, following one path until it came out the other side. Similarly, when we recognize someone, a series of neurons are activated and a memory is formed in our brain. When we meet the same person again, those neurons can fire much faster and using less energy. In vanadium, as the current heated the sample, it caused the VO2 to change state. Once the current passed, the material returned to its initial state. An unexpected find, scientists say. This finding replicates well what happens in the brain, since the VO2 switches acted like neurons. They perfectly mimicked what happens in our brain.
“VO2 seemed to ‘remember’ the first phase transition and anticipate the next,” explains Professor Elison Matioli, director of the POWERlab. “We didn’t expect to see this kind of memory effect, and it has nothing to do with electronic states but with the physical structure of the material. It’s a novel discovery: no other material behaves in this way.”
How long did the memories last?
The researchers found that VO2 is capable of remembering its most recent external stimulus for up to three hours. “In fact, the memory effect could persist for several days, but we currently do not have the necessary instruments to measure it,” says Matioli.
This memory effect reveals a property of vanadium dioxide that was not previously known, which is why this discovery is considered so significant.
Referencia: Mohammad Samizadeh Nikoo, Reza Soleimanzadeh, Anna Krammer, Guilherme Migliato Marega, Yunkyu Park, Junwoo Son, Andreas Schueler, Andras Kis, Philip J. W. Moll, Elison Matioli. Electrical control of glass-like dynamics in vanadium dioxide for data storage and processing. Nature Electronics, 2022; DOI: 10.1038/s41928-022-00812-z
