Microstructural and electrical characteristics of indium-antimony-tellurium chalcogenide alloys for application in phase change memory

Abstract

Ge-Sb-Te ternary alloys have been widely investigated as a phase change material for the phase change nonvolatile memory (PRAM) since they show a reversible transformation between the amorphous and crystalline states, a fast crystallization rate, and a long retention time. Particularly, the $Ge_2Sb_2Te_5$ (GST) alloy has been studied intensively because it has the best conditions to apply to memory devices. Although, the GST is widely known as phase change material, there are several problems such as instability of amorphous state due to low crystallization temperature, high melting temperature and insufficient multi-bit storage capability. To occupy the competitive advantage of PRAM compared to other memory devices, these problems should be overcome. Therefore, many attempts have been made to develop non-GST phase change materials by design the chalcogenide materials. Based on this point, the $In_3Sb_1Te_2$ (IST) alloy was focused on in this study. Actually, the IST has same atomic structure (S.G. $\sharp225$, Fm-3m) and it has nearly same lattice spacing (a=b=c=6.12 $\Aring$) compared with that of the GST (a=b=c=6.03 $\Aring$). In addition, The IST has already known as the optical data storage material. Furthermore, in a recent study, it is revealed that the IST-GST system shows high phase change temperature compared with that of the GST system. Therefore, it is necessary to investigate a possibility of the IST ternary alloys for the application in PRAM. This thesis reports the microstructure and electrical characteristics of the IST ternary alloy for application in PRAM. To investigate its electrical characteristics, PRAM devices were fabricated using the IST and GST ternary alloy. The device had a simple layered structure (bottom electrode/IST/top electrode). The contact region between the bottom electrode and phase change materials was fabricated by the Focused Ion Beam (FIB) method. Reset pulse was generated with Agilent B1101A pulse generator and the c...