For ultra-high density data storage applications, Phase Change Memory (PCM) is considered a potentially disruptive technology. Yet, the long-term reliability of the logic levels corresponding to the resistance states of a PCM device is an important issue for  stable device operation since the resistance levels drift uncontrollably in time. The underlying mechanism for the resistance drift is considered to be structural relaxation and spontaneous crystallization at elevated temperatures. We fabricated nanoscale single active layer-phase change memory cells with three resistance levels corresponding to crystalline, amorphous and intermediate states by controlling the current injection site geometry. For the intermediate state and the reset state, the activation energies and the trap distances have been found to be 0.021 eV and 0.235 eV, 1.31 nm and 7.56 nm, respectively. We attribute the ultra-low and weakly temperature dependent drift coefficient of the intermediate state (ν=0.0016) as opposed to that of the reset state (ν=0.077) as being due to the dominant contribution of the interfacial defects in electrical transport in the case of the mixed phase. Our results indicate that the engineering of interfacial defects will enable a drift-free multi-level PCM device design.  This project has been funded by EU FP7 Marie Curie IRG grant # 256281, TUBITAK grant# 113F385 and Bogazici University Research Fund grant# 6663.

Ozhan Ozatay is an associate professor in the department of physics in Bogazici University, Istanbul-Turkey. He received his BS degree in electrical & electronics engineering and physics from Bogazici  University in 2000, his PhD degree in applied & engineering physics from Cornell University, Ithaca, NY-USA in 2007. He was a post-doctoral fellow in Hitachi Global Storage Technologies, San Jose research labs under the supervision of Dr. Bruce Terris between 2007 and 2009. His research interests include nano-scale phase change memory device characterization and finite element modeling, three dimensional magnetic memory structures and spin transfer torque driven microwave oscillators and detectors.