Researchers at EPFL found that Vanadium Dioxide (VO2), a compound used in electronics, can “remember” everything that has happened to it in the past. This is the first thing that has been found to have this property, but there may be others.

A PhD student at EPFL’s Power and Wide-band-gap Electronics Research Laboratory (POWERlab), Mohammad Samizadeh Nikoo, found something by accident while studying phase changes in Vanadium Dioxide (VO2).

When VO2 is relaxed at room temperature, it enters an insulating phase. However, around 68 °C, it undergoes a sharp insulator-to-metal transition, changing its lattice structure. VO2 usually has a volatile memory, which means that “the material reverts back to the insulating state right after removing the excitation,” says Samizadeh Nikoo.

He wanted to find out how long it takes for VO2 to change from one state to another for his thesis. After doing many measurements, he discovered a memory effect in the material’s structure, which changed the course of his research.

A surprising revelation

Samizadeh Nikoo used an electric current to experiment on a VO2 sample. According to him, “the current moved across the material, following a path until it exited on the other side.” The VO2 changed state as the current heated up the sample. The substance then went back to its initial state when the current had passed. After giving the material a second current pulse, Samizadeh Nikoo discovered that the history of the material had a direct impact on how long it took to change state. Prof. Elison Matioli, the director of the POWERlab, says that the VO2 appeared to “remember” the first phase transition and anticipate the next. 

“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.”

A memory that can hold up to three hours

The researchers discovered that VO2 had a three-hour memory span for the most recent external stimuli. Although Matioli admits that the necessary tools aren’t yet available, the memory effect may last for several days.

The discovery made by the study team is significant since the memory impact that they saw is a fundamental characteristic of the substance itself. Engineers use memory to perform a variety of calculations, and there is a considerable need for materials that could improve computation performance by providing more capacity, speed, and compactness. All three of these criteria are met by VO2. Furthermore, it differs from traditional materials that store data as binary information dependent on the modification of electrical states due to its continuous, structural memory.

To reach their conclusions, the researchers used a variety of measurements. By using the novel method on various materials at other facilities throughout the world, they were able to confirm their findings. The fact that VO2 switches behave exactly like neurons in this discovery perfectly mimics what occurs in the brain.

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