Electronics > EMMA - Emerging Materials for Mass-storage Architectures
Resistive-switching memory (RRAM) has the potential for next-generation high-density non volatile data storage, based on a very small cell area and the 3D-stacking capability. However, many material, operation and integration issues remain open challenges. Aim of the project is to investigate the feasibility RRAMs for enabling new mass-storage memory systems. The research program will study both binary oxides and organic switching materials, while focusing on key challenges like concept scalability, cell integration, reliability and memory architectures.
The project is entering its key stage of nanoscaled cell integration, for both the scaling study and the integration feasibility. System architectures and material studies (electrode impact, reliability optimization) are being developed.
The figure shows simulated temperature profile in the CF during the reset operation. As the voltage increases (from left to right), the temperature due to Joule heating increases, while the filament is thermally dissolved (see the filament edge in green)
Project resultsThanks to the close cooperation among material developers, technology engineers and academic scientist, the project has allowed to gain an unprecedented insight into the RRAM operation mechanism. We clarified that the reset operation (i.e. the transition from low to high resistance in the switching material) is due to a thermally-induced dissolution of a nano-scaled conductive bridge in the dielectric. The reverse (set) transition is instead due to the abrupt local degradation due to the electronic filamentation (aka threshold switching) through the dielectric. Computational models aimed at RRAM TCAD have been accordingly developed.
The outcome of the project has been published in the leading conference on electron device, the International Electron Device Meeting (www.ieee.org/conferences/iedm/), in 2007 and 2008.
 U. Russo, D. Ielmini, C. Cagli, A. L. Lacaita, S. Spiga, C. Wiemer, M. Perego and M. Fanciulli, “Conductive-filament switching analysis and self-accelerated thermal dissolution model for reset in NiO-based RRAM,” IEDM Tech. Dig., 775--778, 2007.
 C. Cagli, D. Ielmini, F. Nardi and A. L. Lacaita, “Evidence for threshold switching in the set process of NiO-based RRAM and physical modeling for set, reset, retention and disturb prediction,” IEDM Tech. Dig., 2008.