Atomic-Scale Observation of Carbon Distribution in High-Performance Carbon-Doped Ge₂Sb₂Te₅ and Its Influence on Crystallization Behavior

Abstract

Phase change memory (PCM) has great potential for the next-generation nonvolatile memory technology, in which Ge2Sb2Te5 (GST) alloy is commonly used. However, poor thermal stability and short device lifetime of GST-based PCM are still the major obstacles. Here, we demonstrate 128 Mb carbon-doped GST (CGST) PCM chips with excellent thermal stability, reduced reset current (0.6 mA), and longer cycle lifetimes (>108 cycles). For the first time, we use the atom probe tomography (APT) technique to investigate the carbon distribution in CGST. APT results reveal the formation of Ge–C, Sb–C, and Te–C bonds in the as-deposited CGST, which leads to the remarkably improved thermal stability of CGST. Moreover, these C-based bonds will break in the recrystallization process and form nanometer-scale carbon clusters in crystalline CGST. Crystalline growth simulation shows that these carbon clusters can also inhibit the growth of the grains, which is responsible for the slower operation speed of the CGST cell compared to that of GST cell. Importantly, owing to the significant inhibition of long-range thermal and electro migrations of Ge, Sb, and Te atoms by carbon clusters, CGST-based chips can achieve a long lifetime.