A comparison of Tc (crystallization temperature) and Tm (melting point) values of various 2D TM chalcogenides; The Tc and Tm values of NbTe4 were defined by the onset temperature of crystallization and melting peaks in this study.
Newswise — PCM is a nonvolatile memory that exploits a phase change material's (PCM) capacity to transition between disordered (amorphous) and tightly packed (crystalline) atomic states. This shift yields an alterable electrical characteristic suitable for data storage and retrieval. Although nascent, PCM has the potential to transform data storage due to its dense storage and expedited data handling. Nevertheless, the intricate manufacturing techniques and intricate switching mechanism of these materials present obstacles to large-scale production.
In recent times, 2D Van Der Waals (vdW) transition metal di-chalcogenides have arisen as a hopeful PCM for phase change memory applications. Presently, a team of scientists from Tohoku University has emphasized the prospective application of sputtering to produce expansive 2D vdW tetra-chalcogenides. Employing this method, they produced and recognized a remarkably encouraging substanceーniobium telluride (NbTe4)ーthat demonstrates an extremely low melting point of about 447 ºC (initial temperature), differentiating it from alternative TMDs.
"Sputtering is a broadly employed method that encompasses the deposition of slender films of a substance onto a substrate, enabling meticulous regulation of film thickness and composition," clarifies Yi Shuang, a co-author of the paper and an assistant professor at Tohoku University's Advanced Institute for Materials Research.
"The NbTe4 films we deposited initially lacked a defined crystalline structure, but through annealing at temperatures surpassing 272 ºC, they could be transformed into a crystalline phase characterized by a layered 2D arrangement."
Diverging from typical amorphous-crystalline phase change materials like Ge2Sb2Te5 (GST), NbTe4 exhibits an extraordinary blend of a low melting point and a high temperature for crystallization. This exceptional combination presents advantages such as decreased reset energies and enhanced thermal stability while in the amorphous phase.
Following the production of NbTe4, the researchers proceeded to assess its performance in switching. Remarkably, it showcased a notable reduction in operational energy when compared to traditional phase-change memory compounds. The estimated temperature for retaining data over a span of 10 years was found to be as high as 135 ºC, surpassing the 85 ºC threshold of GST. This discovery suggests outstanding thermal stability and implies that NbTe4 could be employed in high-temperature settings like the automotive industry. Additionally, NbTe4 exhibited an impressive switching speed of approximately 30 nanoseconds, further underscoring its potential as a next-generation phase change memory technology.
Shuang enthusiastically remarks, "Our findings have truly expanded the horizons for the advancement of high-performance phase change memories. NbTe4, with its unique combination of a low melting point, high crystallization temperature, and exceptional switching capabilities, emerges as the ideal material to tackle the existing challenges encountered by current phase change memory technologies."
Details of the group's discovery were published in the journal Advanced Materials on June 20, 2023.
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