Unveiling structural characteristics for ultralow resistance drift in BiSb-Ge2Sb2Te5 materials for phase-change neuron synaptic devices

Abstract

Phase-change materials are among the leading candidates that satisfy the need for in-memory computing or computational memory. Ge2Sb2Te5 (GST) is the representative material among them, but amorphous resistance drift in GST limits its cyclable stability. Here, we optimize the properties and microstructure of a GST material by introducing a BiSb phase. Results reveal that the amorphous resistance of GST decreases after the addition of BiSb and the drift coefficient can be reduced to 0.004 because of the decreased disorder in the amorphous state. Further analysis of microstructural characteristics reveals that the distribution of the Bi-Sb phase restrains the diffusion of Sb/Te element and suppresses the formation of voids in GST phases. These features stabilize the nanostructures and suppress resistance drift to a certain extent because of the dual-phase coexistence. Moreover, the conduction of GST compounds changes from a p-type to an n-type, originating from n-type BiSb precipitations. Notably, resistance drift can be further decreased through liquid nitrogen treatment, which restricts atomic mobility in small volumes, changes electron binding energy, and improves the stability of amorphous phases during structural relaxation. Decrease in resistance drift originates from the narrowing of the band gap from 0.65 eV for GST to 0.33 eV for (BiSb)5.1(GST)94.9. Thus, our present research shows that doping GST with BiSb is one of the effective means to obtain ultralow resistance shift in phase-change neuron synaptic devices.