EnTiered-ReRAM: An Enhanced Low Latency and Energy Efficient TLC Crossbar ReRAM Architecture

Resistive Random Access Memory (ReRAM) is promising to be employed as high density storage-class memory due to its crossbar array and Triple-Level Cell (TLC) structures. However, TLC crossbar ReRAM suffers from high write latency and energy due to three unique challenges: (1) The crossbar array structure incurs IR drop issues. (2) The TLC structure requires iterative program-and-verify (P&V) procedure. (3) The resistance drift problem needs short interval scrub to avoid uncorrectable soft errors. In this article, to overcome the challenges of TLC crossbar ReRAM, we propose an enhanced low latency and energy efficient TLC crossbar ReRAM architecture, called EnTiered-ReRAM. The proposed EnTiered-ReRAM is composed of four components, including EnTiered-crossbar design, Compression-based Incomplete Data Mapping (CIDM), Compression-based Flip Scheme (CFS), and Compression-based Error Correction Code (CECC). Specifically, based on the observation that our previously proposed Tiered-crossbar design still suffers from large IR drops along bitlines in the far segments due to the long length of bitlines, EnTiered-crossbar partitions each crossbar array into two halves along bitlines, and then splits each bitline of the half crossbar array into the near and far segments by an isolation transistor, which thoroughly mitigates the IR drop issues. Then we use our previously proposed CIDM and CFS in the near and far segments of EnTiered-crossbar arrays to further decreases the write latency and energy. In addition, CECC is deeply coupled with CIDM and CFS. CECC dynamically employs the most appropriate ECC capability according to the remaining space of each cache line after CIDM or CFS encoding, which effectively improves the scrub interval and performance/energy with insignificant space overhead. The evaluation results show that, compared with an aggressive baseline, EnTiered-ReRAM can improve the system performance by 56.3% and reduce the energy consumption by 60.6% on average.