Phase-Change Random Access Memory With Multilevel Resistances Implemented Using a Dual Phase-Change Material Stack

This paper investigates the multilevel behavior of phase-change random access memory devices with a dual phase-change material (PCM) stack, i.e., two PCMs stacked on one another. The dual PCM stack comprises of a Ge
₂
Sb
₂
Te
₅
(GST) layer and a top PCM layer sandwiching a SiN barrier layer. The top PCM layer was varied in three different splits: Ag
_0.5
In
_0.5
Sb
₃
Te
₆
(AIST), Ge
₁
Sb
₄
Te
₇
(GST147), and nitrogen-doped GST (NGST). Extensive electrical characterization and statistical analysis were performed. The intrinsic properties of AIST, GST147, and NGST were used to explain the differences in electrical performances of the three multilevel device splits. The AIST/SiN/GST device split was found to have had the best electrical performance. The difference in electrical resistivities and thermal conductivities played a major role in the power consumption as well as the resistance values of the three multilevel states in these dual PCM multilevel devices.