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Revolutionary Amorphization Method Advances Phase-Change Memory Technology
Amorphous solids, such as glass, are characterized by their lack of ordered atomic structures, which result in a disorganized arrangement akin to grains of sand on a beach. Traditionally, transforming materials into amorphous states—a process referred to as amorphization—demands substantial energy input. The prevalent method involves the melt-quench technique, where a material is heated to a liquid state and then cooled quickly to prevent the atoms from forming a crystalline lattice.
However, researchers from the University of Pennsylvania School of Engineering and Applied Science, the Indian Institute of Science, and the Massachusetts Institute of Technology have pioneered a novel approach for amorphizing a specific material: indium selenide (In2Se3) wires. This innovative technique requires dramatically less energy, reportedly one billion times lower in power density, as detailed in their recent publication in Nature. Such advancements have the potential to expand the use of phase-change memory (PCM) technology—a cutting-edge data storage solution that could revolutionize devices like smartphones and computers.
PCM technology operates on the principle of toggling a material between amorphous and crystalline states, analogous to an on/off switch. Despite its promise, widespread commercial adoption has been hindered by the substantial energy required for these transitions. Ritesh Agarwal, a distinguished professor at Penn Engineering and a senior author on the paper, stated, “The energy demands have been a significant barrier to the broader implementation of phase-change memory devices.”
Agarwal’s research team has been investigating alternatives to the conventional melt-quench method for over ten years. Their journey began with the discovery in 2012 that applying electrical pulses could cause amorphization in germanium-antimony-tellurium alloys without melting.
One of the co-authors of the new study, Gaurav Modi, began exploring indium selenide’s unique features, including its ferroelectric and piezoelectric properties, during his doctoral tenure in Materials Science and Engineering at Penn Engineering. Surprisingly, he stumbled upon the new amorphization method while passing an electric current through In2Se3 wires. To his astonishment, the wires ceased to conduct electricity as parts of them transitioned to an amorphous state. “I initially thought I might have caused irreparable damage to the wires. Typically, one would need electrical pulses to achieve amorphization, yet in this case, a continuous current induced a disruption in the crystalline structure,” Modi remarked.
Resolving this unexpected phenomenon required considerable time and investigation. Agarwal enlisted the help of Pavan Nukala, a former graduate student now at the Indian Institute of Science, to utilize advanced in situ microscopy techniques to delve deeper into the observed changes. “We needed to meticulously analyze this process to understand the interplay of various properties in In2Se3,” Nukala noted. They discovered that the combination of its two-dimensional nature, along with its ferroelectric and piezoelectric characteristics, facilitates a low-energy method for amorphization.
The research revealed that the amorphization process is analogous to both an avalanche and an earthquake. Initially, microscopic segments—measured on the scale of nanometers—within the In2Se3 wires start to amorphize in response to electrical deformation. The material’s piezoelectric traits, coupled with its layered configuration, enable the current to destabilize portions of the layers, akin to snow shifting on a slope.
Once a threshold is crossed, these localized deformations proliferate rapidly throughout the wire. As regions of distortion collide, they generate sound waves, reminiscent of seismic activity, which propagate through the substance. This phenomenon, termed as an “acoustic jerk,” promotes further deformation, linking multiple tiny amorphous regions into more extensive areas—measured in micrometers—and resembling an avalanche gathering force down a mountainside. “Witnessing these different phenomena interact across various scales is truly fascinating,” shared Shubham Parate, an IISc doctoral student and co-first author of the paper.
This collaborative research lays the groundwork for future advances in material science. “Our findings open a new avenue for exploring structural transformations in materials driven by these unique properties. The implications for developing low-power memory devices are significant,” concluded Agarwal.
This research was supported by various organizations, including the U.S. Office of Naval Research, the National Science Foundation, and the Government of India’s Anusandhan National Research Foundation, leveraging advanced microscopy facilities at IISc.
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