SECRET: Selective error correction for refresh energy reduction in DRAMs

DRAMs are used as the main memory in most computing systems today. Studies show that DRAMs contribute to a significant part of overall system power consumption. Therefore, one of the main challenges in low-power DRAM design is the inevitable refresh process. Due to process variation, memory cells exhibit retention time variations. Current DRAMs use a single worst-case refresh period. Prolonging refresh intervals introduces retention errors. Previous works adopt conventional ECC (Error Correcting Code) to correct retention errors. These approaches introduce significant area and energy overheads. In this paper, we propose a novel error correction framework for retention errors in DRAMs, called SECRET (Selective Error Correction for Refresh Energy reducTion). The key observation we make is that retention errors can be treated as hard errors rather than soft errors, and only few DRAM cells have large leakage. Therefore, instead of equipping error correction capability in all memory cells as existing ECC schemes, we only allocate error correction information to leaky cells under a refresh interval. Our SECRET framework contains two parts, an off-line phase to identify memory cells with retention errors given a target error rate, and a low-overhead error correction mechanism. The experimental results show that the proposed SECRET framework can reduce refresh power by 87.2%, and overall DRAM power by 18.57% with negligible area and performance overheads.