Researchers from École Polytechnique Fédérale de Lausanne (EPFL) have discovered that vanadium dioxide (VO2) is capable of "remembering" the entire history of previous external stimuli.
Vanadium dioxide marks the first material EPFL researchers have discovered that identified as possessing this property.
The study was published in Nature today.
Mohammad Samizadeh Nikoo, a Ph.D. student at EPFL's Power and Wide-band-gap Electronics Research Laboratory (POWERlab), made a chance discovery during his research on phase transitions in vanadium dioxide (VO2).
As per the study, VO2 has an insulating phase when relaxed at room temperature and undergoes a steep insulator-to-metal transition at 68 °C, where its lattice structure changes.
Under normal conditions, VO2 displays volatile features. "The material reverts to the insulating state right after removing the excitation," said Mohammad Samizadeh Nikoo.
During the experiment, Samizadeh Nikoo applied electric current to a sample of VO2. "The current moved across the material, following a path until it exited on the other side," he said.
After the current passed in the first application, the material returned to its state, and after the second application of Samizadeh Nikoo, the material began to show "remembering" features.
"The VO2 seemed to 'remember' the first phase transition and anticipate the next," explains Prof. Elison Matioli, who heads the POWERlab. "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 researchers went on to find that VO2 is capable of remembering its most recent external stimulus for up to three hours.
"The memory effect could in fact persist for several days, but we don't currently have the instruments needed to measure that," says Prof. Matioli.
The research team's discovery is considered to be quite significant. The memory effect reveals a property of vanadium dioxide not previously known.
Engineers depend on memory to perform calculations of all kinds, and materials that could enhance the calculation process by offering greater capacity, speed, and miniaturization are in high demand.
Metal–oxide–semiconductor junctions are the building blocks of modern electronics and can provide a variety of functionalities, from memory to computing. The technology, however, faces constraints in terms of further miniaturization and compatibility with post–von Neumann computing architectures. Manipulation of structural—rather than electronic—states could provide a path to ultra scaled low-power functional devices, but the electrical control of such states is challenging. Here we report electronically accessible long-lived structural states in vanadium dioxide that can provide a scheme for data storage and processing. The states can be arbitrarily manipulated on short timescales and tracked beyond 10,000 s after excitation, exhibiting features similar to glasses. In two-terminal devices with channel lengths down to 50 nm, sub-nanosecond electrical excitation can occur with an energy consumption as small as 100 fJ. 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.