Professor Eric Pop's lab - Pop Lab - took a long shot adapting phase-change memory (PCM) to plastic substrates – turns out the energy-efficiency significantly improved compared to PCM on conventional silicon substrates.
Phase change materials leverage changes in structure into differences in electrical resistance that are attractive for computer memory and processing applications. Khan et al. developed a flexible phase change memory device with layers of antimony telluride and germanium telluride deposited directly on a flexible polyimide substrate. The device shows multilevel operation with low switching current density. The combination of phase change and flexible mechanical properties is attractive for the large number of emerging applications for flexible electronics.
"It's the same atoms as conventional phase-change memory but in beautiful striped alternating thin layers, also known as a superlattice," says Professor Eric Pop.
Eric's group put arrays of memory cells made of superlattices of alternating layers of antimony telluride and germanium telluride on flexible plastic substrates. They were curious whether they could make it work—flexible memory is a key enabling technology for electronic skin, lightweight environmental sensors, and other unconventional electronics. Once grad student Asir Intisar Khan and postdoc Alwin Daus figured out how to make these devices at temperatures that would not melt the polyimide substrate, the researchers were surprised by what they found.
"The flexible substrate provides an extra advantage we did not anticipate," reports Eric Pop. The current density required to switch the flexible memory cells is 10 to 100x lower than any previously reported phase-change memory, and the memory cells maintain their performance when the substrate is bent. After seeing the results, the team was "scrambling," he continues. "Why is this better?" The Stanford group believes that the layers in the superlattice, the cell's "pore-like" design, as well as the insulating properties of the plastic substrate, help confine the energy applied to the memory cells, making them heat up more efficiently and spurring a phase change at lower electrical currents.
Read their paper in Science, "Ultralow–switching current density multilevel phase-change memory on a flexible substrate," 10 September, 2021.
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Stanford Energy, "Stanford discovery could pave the way to ultrafast, energy-efficient computing".