A Novel Built-In Self-Repair Approach for Embedded RAMs

In this paper, a novel built-in self-repair approach, block-level reconfiguration architecture, is proposed. Our approach is based on the concept of divided word line (DWL) for high-capacity memories, including SRAMs and DRAMs. This concept is widely used in low-power memory designs. However, the characteristics of divided word line memories have not been used for fault-tolerant applications. Therefore, we propose the block repair fault-tolerant architecture based on the structure of DWL for high-capacity memories. The redundant rows of a memory array are divided into blocks and reconfiguration is performed at the block level instead of the traditional row level. Our fault-tolerant architecture can improve the yield for memory fabrication significantly. Moreover, the characteristics of low power and fast access time of DWL memories are also preserved. The reconfiguration mechanism of our block repair architecture requires negligible hardware overhead. According to experimental results, the hardware overheads are less than 0.73% and 0.48% for 256-Kbit SRAMs and 8-Mbit DRAMs, respectively. The repair rate of our approach with previous memory repair algorithms is compared. It is found that block repair approach improves repair rate significantly. The yield improvement over traditional row-based approaches is also analyzed. Simulated results show that the present approach can significantly improve fabrication yield.