Thermal-stability optimization of Al2O3/Cu–Te based conductive-bridging random access memory systems

Abstract

In this article we study the thermal stability of Al2O3\\Cu–Te bi-layers up to temperatures used in the back-end-of-line integration process flow of conductive-bridging random-access-memory (CBRAM) technology. We investigate the temperature dependence of the microstructure and morphology of the CuxTe1−x layers for 0.2<x<0.8. For x>0.7, phase separation is observed for as-deposited layers, resulting in rough morphology. Te-rich CuxTe1−x layers (x<0.5) show large segregation processes during post-deposition annealing. Cu–Te phase restructuration phenomena are also observed during annealing in the range 0.5<x<0.7, however affecting little the roughness of the layer. On the other hand, both the Cu and Te elements diffuse into the Al2O3 layer already at moderate temperatures. These in-diffusion processes are efficiently reduced by inserting thin Ti layer at the Al2O3\\Cu–Te interface. By means of secondary ion-mass spectroscopy analysis, we show that the thickness of the Ti layer allows obtaining either Cu-barrier (6nm-thick Ti) or Cu-buffer (3nm-thick Ti) properties. The optimized thermal stability achieved both by tuning the Cu–Te composition and by inserting 3nm-thick Ti layer results in excellent and thermally stable CBRAM functionality after stack integration.