The new candidate for phase-change memory (PCM), which combines the best of short-term memory and long-term storage, consumes far less power than previously identified materials.
Scientists may have accidentally overcome a major barrier to smoothening the adoption of next-generation data-storage technologies.
Using a unique material called indium selenide (In2Se3), researchers say they discovered a technique for lowering the energy requirements of phase-change memory (PCM) — a technology capable of storing data without a constant power supply — by up to 1 billion times.
The breakthrough is a step toward overcoming one of the biggest challenges in PCM data storage, potentially paving the way for low-power memory devices and electronics, the researchers said in a study published Nov. 6 in the journal Nature.
PCM is a leading candidate for universal memory — computing memory that can replace both short-term memory like random access memory (RAM) and storage devices like solid-state drives (SSDs) or hard drives. RAM is fast but needs significant physical space and a constant power supply to run, while SSDs or hard drives are much denser and can store data while computers are turned off. Universal memory combines the best of both.
It works by toggling materials between two states: crystalline, where atoms are neatly ordered, and amorphous, where atoms are randomly arranged. These states correlate to binary 1s and 0s, encoding data via switches in states.
However, the "melt-quench technique" used to toggle these states — which involves heating and rapidly cooling PCM materials — requires significant energy, making the technology expensive and difficult to scale. In their study, the researchers found a way to bypass the melt-quench process entirely by instead inducing amorphization through an electrical charge. This slashes PCM's energy requirements and potentially opens the door to broader commercial applications.
"One of the reasons why phase-change memory devices haven't reached widespread use is due to the energy required," study author Ritesh Agarwal, a professor of materials science and engineering at Penn Engineering, said in a statement. The potential of these findings for designing low-power memory devices is "tremendous," he said.
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The researchers' discovery hinges on the unique properties of indium selenide, a semiconductor material with both "ferroelectric" and "piezoelectric" characteristics. Ferroelectric materials can spontaneously polarize, meaning they can generate an internal electric field without needing an external charge. Piezoelectric materials, by contrast, physically deform when they are exposed to an electric charge.
While testing the material, the researchers observed that sections of it amorphized when they were exposed to a continuous current. What's more, this happened entirely by chance.
"I actually thought I might have damaged the wires, study co-author Gaurav Modi, a former doctoral student in materials science and engineering at Penn Engineering, said in the statement. "Normally, you would need electrical pulses to induce any kind of amorphization, and here a continuous current had disrupted the crystalline structure, which shouldn't have happened."
Further analysis revealed a chain reaction triggered by the semiconductor's properties. This begins with tiny deformations in the material caused by the current that triggers an "acoustic jerk" — a sound wave similar to seismic activity during an earthquake. This then travels through the material, spreading amorphization across micrometer-scale regions in a mechanism the researchers likened to an avalanche gathering momentum.
The researchers explained that various properties of indium selenide — including its two-dimensional structure, ferroelectricity and piezoelectricity — work together to enable an ultra-low-energy pathway for amorphization triggered by shocks. This could lay the groundwork for future research around "new materials and devices for low-power electronic and photonic applications," they wrote in the study.
"This opens up a new field on the structural transformations that can happen in a material when all these properties come together," Agarwal said in the statement.
