Design for ReRAM-based main-memory architectures

With the anticipated scaling issues of DRAM memory technology and the increased need for higher density and bandwidth, several alternative memory technologies are being explored for the main memory system. One promising candidate is a variation of Resistive Random-Access Memory (ReRAM) which implements the memory bit-cells on Back-End-of-Line (BEOL) layers. This allows for fabrication of the processor logic and ReRAM main-memory to be implemented on the same chip. As the memory cells can be stacked vertically, the density of this memory also scales to 1-4F2. This tight integration allows for a high amount of parallelism between the processor and memory systems and delivers low access granularity without sacrificing density or bandwidth. In this paper, we explore physical integration of a processor with a ReRAM-based main-memory system using the bitcell technology developed by Crossbar, Inc. We present Crossbar's ReRAM technology characteristics, the methodology and assumptions used for our digital implementation, and summarize the results obtained for different array configurations. Our results indicate that, in addition to the overhead for the ReRAM access circuits, the overall integrated area increases by 11% to 19%, based on the configuration at the 45nm process node. Results from architectural simulation comparing DRAM with ReRAM based architecture are presented.