Fabrication of stable multi-level resistance states in a Nb-doped Ge2Sb2Te5 device

Abstract

We report a phase-change memory with controllable multiple-resistance states. Many chemical doping studies have been performed on phase-change materials; however, few have focused on chemical bonding between the doped and host atoms. Phase changes in the doped system exhibited strong bond-length dependences between the doped element X and Te in X–Te polyhedrons. The most stable doped system was when the bond length was similar to that of Ge–Te in Ge₂Sb₂Te₅ (GST). We used Nb doping in GST for a stable multi-level state for phase-change memory applications because of the similar Nb–Te and Ge–Te bond lengths. Nb-doped GST enhanced structural stability and resulted in a continuum of multi-level resistance states with low resistance drift. Ab initio molecular-dynamics simulations were performed to model the local motif in amorphous Nb-doped GST. The phase-change speed in GST was not affected by Nb doping because the dominating octahedral motif was unchanged. Atomic mobility was suppressed, leading to enhanced stability in the amorphous state. Nb-GST thin films thus had significant advantages for multi-level PCM applications.