Thermal-aware, heterogeneous materials for improved energy and reliability in 3D PCM architectures.

The properties of Phase-Change Memory (PCM) are defined in large part by the different chalcogenide materials employed. As the GeTe and Sb2Te3 ratios in the materials are changed, the operating temperatures needed for the phase change are also variable. Motivated by this phenomenon, we study the potential of exploiting different material compositions to achieve different trade-offs among the optimal operating temperatures, energy efficiency, write endurance and write latency. Specifically, we study the trade-offs for energy efficiency and lifetime in the scenario of using PCM materials for all layers of a 3D stack memory. Rather than a "one-memory-fitsall" approach, we propose Heterogeneous 3D PCM architectures by tailoring the Ge-Sb-Te ratios of PCM in concert with both the location and the intended function of these memories within the 3D stack. By varying the material compositions and their operating temperatures in correspondent with the non-uniform heat distribution across the stack, the heterogeneous PCM architectures improve the programming energy by up to 3.5X compared to the best homogeneous configuration. Moreover, the diversity in material compositions can also be exploited to protect error-correcting codes (ECC) by storing them in PCM materials with lower operating temperatures, which drastically reduces ECC early failures and brings a 30% improvement in the lifetime of the entire memory system. This architectural study attempts to make the case for exploring the whole material spectrum and the manufacturing cost associated with that.