The new material shows promise for next-generation memory technology


July 10, 2023

(Nanowerk News) Phase change memory is a type of nonvolatile memory that takes advantage of the ability of a phase change material (PCM) to switch from an amorphous state, i.e., in which the atoms are disordered, to a crystalline state, i.e., in which the atoms are tightly packed close together. This change produces reversible electrical properties that can be engineered to store and retrieve data.

While this field is still in its infancy, phase change memory has the potential to revolutionize data storage due to its high storage density, and faster read and write capabilities. But still, the complex switching mechanisms and complex fabrication methods associated with these materials pose challenges for mass production.

In recent years, Van Der Waals (vdW) two-dimensional transition metal (2D) di-chalcogenides have emerged as promising PCMs for use in phase-change memory. Now, a group of researchers from Tohoku University have highlighted the potential of using sputtering to make widespread 2D vdW tetra-chalcogenides. Using this technique, they generated and identified a very promising material ーniobium telluride (NbTe4)ーwhich exhibits a very low melting point of around 447 °C (initial temperature), distinguishing it from other TMDs. Comparison of Tc (crystallization temperature) and Tm (melting point) values ​​of various 2D TM chalcogenides Comparison of Tc (crystallization temperature) and Tm (melting point) values ​​of various TM 2D chalcogenides; Tc and Tm values ​​from NbTe4 determined by the initial temperature of crystallization and the melting peak in this study. (Image: Yi Shuang et al.)

“Sputtering is a widely used technique that involves depositing a thin film of a material onto a substrate, enabling precise control over film thickness and composition,” explained Yi Shuang, assistant professor at Tohoku University’s Institute of Materials Research and one of the authors of the paper. (Advanced Materials, “NbTe4 Phase Change Materials: Breaking the Phase Change Temperature Equilibrium in 2D van der Waals Transition-metal Binary Chalcogenide”). “NbTe that we deposited4 the film is initially amorphous, but can crystallize into a 2D layered crystalline phase by annealing at temperatures above 272 °C.”

Unlike conventional amorphous crystal PCM, such as Ge2sb2That5 (GST), NbTe4 exhibits low melting point and high crystallization temperature. This unique combination offers reduced reset energy and increased thermal stability of the amorphous phase. Selected area electron diffraction and cross-sectional TEM images of deposited and 350 C annealed NbTe4 thin films Selected area electron diffraction and cross-sectional TEM images of precipitated and 350 °C annealed NbTe4 thin film. (Image: Yi Shuang et al.)

After creating NbTe4, the researchers then evaluated its switching performance. It exhibits a significant reduction in operating energy compared to conventional phase change memory compounds. Estimated 10 year data retention temperature found to be as high as 135 °C – better than 85 °C GST – indicating excellent thermal stability and possibly NbTe4 for use in high temperature environments such as in the automotive industry. Additionally, NbTe4 demonstrated a fast switching speed of around 30 nanoseconds, further highlighting its potential as the next generation of phase change memory.

“We have opened up new possibilities for developing high-performance phase change memory,” added Shuang. “With NBTE4Its low melting point, high crystallization temperature and excellent switching performance position it as an ideal material to overcome some of the challenges faced by today’s PCM.”


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