Yield and Reliability Improvement Techniques for Emerging Nonvolatile STT-MRAM

The emerging spin transfer torque magnetic random access memory (STT-MRAM) promises many attractive features, such as nonvolatile, high speed and low power etc, which enable it to be a promising candidate for the next-generation logic and memory circuits. However with the continuous scaling technology process, the chip yield and reliability of STT-MRAM face severe challenges due to the increasing permanent and transient faults. Due to the intrinsic fault features and the targeted application requirements of STT-MRAM, traditional fault tolerant design solutions, such as error correction code (ECC), redundancy repair (RR), and fault masking (FM) techniques, cannot be employed straightforwardly for STT-MRAM. In this paper, we propose a synergistic technique framework, named sECC, that integrates both the ECC and FM techniques to address simultaneously the permanent and transient faults. With such approach, permanent faults are masked while transient faults are corrected with the same codeword. Moreover taking into consideration the fact that most permanent faults are sparse [about 60%-70% single isolated faults (SIFs)], we propose further integrating the RR and sECC (named iRRsECC) to optimize the system performance. In this scenario, all the SIFs are masked and the transient faults are corrected with the proposed sECC, while other permanent faulty types (e.g., faulty rows or columns) are repaired with redundant rows or columns. A simulation tool is developed to evaluate the proposed techniques and the evaluation results show their good performance in terms of repair rate and hardware overhead.