A compound used in electronics known as vanadium dioxide (VO2) has a memory like the human brain, according to a new study led by the Ecole Polytechnique Federale de Lausanne. The experts discovered that VO2 is capable of “remembering” the entire history of previous external stimuli. This is the only material that is known to possess this property.
Mohammad Samizadeh Nikoo is a PhD student at EPFL’s Power and Wide-band-gap Electronics Research Laboratory (POWERlab). He stumbled upon the fascinating capability of VO2 while observing phase transitions of the inorganic compound.
When relaxed at room temperature, vanadium dioxide experiences an insulating phase. At 68 °C, the compound undergoes a complete structural change during an insulator-to-metal transition.
Furthermore, according to Nikoo, VO2 exhibits a volatile memory. “The material reverts back to the insulating state right after removing the excitation.”
Nikoo set out to discover how long it takes for VO2 to transition from one state to another. After taking hundreds of measurements, he recognized a memory effect in the material’s structure. Nikoo then applied an electric current to a sample of VO2
“The current moved across the material, following a path until it exited on the other side.” As the current heated up the material, it caused the VO2 to change state. Once the current had passed, the material returned to its initial state.
Next, when Nikoo applied a second current pulse to the material, he found that the time it took to transition was directly linked to the history of the material.
“The VO2 seemed to ‘remember’ the first phase transition and anticipate the next,” explained Professor 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.”
Ultimately, the experts determined 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,” said Professor Matioli.
The study is published in the journal Nature Electronics.
Image Credit: POWERlab / 2022 EPFL