Scientists have discovered the first known material that is capable of remembering previous external stimuli—the first known memory material—despite not having an apparent mechanism that would be able to store any information. The discovery could be used as an alternative to silicon for use in powerful data processing and storage devices.
This special property of the compound, vanadium dioxide (VO2), was discovered by researchers at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL), while investigating the idea that the substance could be used as an alternative, or perhaps a successor, to silicon in the electronic components that power our computers and mobile devices, as VO2 tends to perform better in those applications. The compound is unusual in that below 68°C (154.4°F) VO2 acts as an electrical insulator, but above that temperature it turns into a metal with good electrical conductivity.
This stark change in properties is referred to as a metal-insulator transition: above the critical temperature, the atoms in the substance arrange themselves in a lattice that can conduct electricity; below that temperature and the atoms fall back into an arrangement that prevents the passage of electrons.
It was while investigating this peculiar quality that the researchers found that VO2 behaved as if it remembered prior experiments: when first exposed to an electrical current, the test material heated up and allowed the current to flow; after the current was removed it cooled and returned to its insulative state.
But when the experiment was repeated the vanadium dioxide acted as if it remembered the phases that it experienced from its previous electrical exposure, switching between the various states faster than when the current was first passed through it. The team found that the VO2 could “remember” these states for up to three hours, but they also suspect that the effect could potentially last for days.
“The VO2 seemed to ‘remember’ the first phase transition and anticipate the next,” explains EPFL electrical engineer Elison Matioli. “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. It’s a novel discovery: no other material behaves in this way.”
The intriguing thing about this discovery is that this memory effect is a property inherent to vanadium dioxide itself, without having to arrange the compound into circuits or other mechanisms. Additionally, the memory effect exhibited by VO2 could be used to construct circuits that perform both memory and information processing functions, called neuromorphics, circuits that are more like the neurons in a biological brain than typical silicon-based microchips.
“These glass-like functional devices could outperform conventional metal-oxide-semiconductor electronics in terms of speed, energy consumption and miniaturization, as well as provide a route to neuromorphic computation and multilevel memories,” explains research team lead Mohammad Samizadeh Nikoo, an electrical engineer at EPFL.
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