Shocking New Memory Tech: Crystal-to-Glass Transformation Using a Billion Times Less Energy
A breakthrough discovery in indium selenide could revolutionize memory storage technology by enabling crystalline-to-glass transitions with minimal energy.
Researchers found that this transformation can occur through mechanical shocks induced by continuous electric current, bypassing the energy-intensive melting and quenching process. This new approach reduces energy consumption by a billion times, potentially enabling more efficient data storage devices.
Revolutionary Discovery in Memory Storage Materials
In a groundbreaking study published on November 6 in Nature, researchers reveal that indium selenide, a unique material, can “shock” itself into transforming from a crystalline to a glassy phase with minimal power. This transformation process, essential to memory storage in devices like CDs and computer RAM, requires a billion times less energy than the conventional melt-quench method traditionally used to convert crystals into glass.
The study involved a collaborative team of scientists from the Indian Institute of Science (IISc), the University of Pennsylvania School of Engineering and Applied Science (Penn Engineering), and the Massachusetts Institute of Technology (MIT).
Understanding the Glass Transition in Memory Devices
Glasses behave like solids but lack the typical periodic arrangement of atoms. During glassmaking, a crystal is liquefied (melted) and then suddenly cooled (quenched) to prevent the glass from becoming too organized. This melt-quench process is also used in CDs, DVDs, and Blu-ray discs – laser pulses are used to heat and quench a crystalline material to the glassy phase very quickly in order to write data; reversing the process can erase data. Computers use similar materials called phase-change RAMs, in which information is stored based on the type of resistance – high versus low – offered by the glassy and crystalline states.
The problem, however, is that these devices are very power-hungry, especially during the writing process. The crystals need to be heated to temperatures exceeding 800oC and suddenly cooled. If there is a way to convert the crystal directly to glass without the intermediate liquid phase, the power required for memory storage can significantly be reduced.
Discovery of Low-Energy Amorphization in Indium Selenide
In the study, the team discovered that when electric current was passed through wires made of indium selenide, a 2D ferroelectric material, long stretches of the material suddenly amorphized into glass. “This was extremely unusual,” says Gaurav Modi, former PhD student at Penn Engineering and one of the first authors. “I actually thought that I might have damaged the material. 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.”
Modi and Ritesh Agarwal, Srinivasa Ramanujan Distinguished Scholar in Materials Science and Engineering (MSE) at Penn Engineering, worked with Pavan Nukala, Assistant Professor at the Centre for Nano Science and Engineering (CeNSE), IISc and his PhD student Shubham Parate to closely track this process – from atomic to micrometer length scales – under an electron microscope.
“Over the past few years, we have developed a suite of in situ microscopy tools here at IISc,” Nukala explains. “When Ritesh told me about this unusual observation, we decided that it was time to put these tools to the test.”
Sliding Layers and Domain Formation: The Earthquake Effect
What the team found was that when a continuous current is passed parallel to the material’s 2D layers, the layers slide against each other in different directions. This causes the formation of many domains – tiny pockets with a specific dipole moment – bound by defective regions that separate the domains. When multiple defects intersect in a small nanoscopic region, like too many holes punched in a wall, the structural integrity of the crystal collapses to form glass locally.
These domain boundaries are like tectonic plates. They move with the electric field, and when they collide against each other, mechanical (and electrical) shocks are generated akin to an earthquake. This earthquake triggers an avalanche effect, causing disturbances far away from the epicenter, creating more domain boundaries and resulting glassy regions, which in turn spawns more earthquakes. The avalanche stops when the entire material turns into glass (long-range amorphisation).
“It’s just goosebumps stuff to see all of these factors come to life and play together, at different length scales in an electron microscope,” says Parate, one of the first authors.
Nukala points out that multiple unique properties of indium selenide – its 2D structure, ferroelectricity, and piezoelectricity – all come together to allow this ultralow energy pathway for amorphization through shocks. “We are going to push this to the next level to integrate these devices on CMOS platforms,” he adds.
Implications for Future Phase-Change Memory Devices
“One of the reasons why phase-change memory (PCM) devices haven’t reached widespread use is due to the energy required,” says Agarwal. Such an advancement could unlock a wider range of PCM applications that could transform data storage in devices, from cell phones to computers.
Reference: “Electrically driven long-range solid-state amorphization in ferroic In2Se3” by Gaurav Modi, Shubham K. Parate, Choah Kwon, Andrew C. Meng, Utkarsh Khandelwal, Anudeep Tullibilli, James Horwath, Peter K. Davies, Eric A. Stach, Ju Li, Pavan Nukala and Ritesh Agarwal, 6 November 2024, Nature.
DOI: 10.1038/s41586-024-08156-8