NbTe₄ Phase-Change Material: Breaking the Phase-Change Temperature Balance in 2D Van der Waals Transition-Metal Binary Chalcogenide.

Abstract

2D van der Waals (vdW) transition metal di-chalcogenides (TMDs) have garnered significant attention in the nonvolatile memory field for their tunable electrical properties, scalability, and potential for phase engineering. However, their complex switching mechanism and complicated fabrication methods pose challenges for mass production. Sputtering is a promising technique for large-area 2D vdW TMD fabrication, but the high melting point (typically T_m > 1000 °C) of TMDs requires elevated temperatures for good crystallinity. This study focuses on the low-T_m 2D vdW TM tetra-chalcogenides and identifies NbTe₄ as a promising candidate with an ultra-low T_m of around 447 °C (onset temperature). As-grown NbTe₄ forms an amorphous phase upon deposition that can be crystallized by annealing at temperatures above 272 °C. The simultaneous presence of a low T_m and a high crystallization temperature T_c can resolve important issues facing current phase-change memory compounds, such as high Reset energies and poor thermal stability of the amorphous phase. Therefore, NbTe₄ holds great promise as a potential solution to these issues.