Alternative Encoding: A Two-Step Transition Reduction Scheme for MLC STT-RAM Cache

Although multiple-level-cell (MLC) STT-RAM increases data density, it suffers from the two-step transition (TT) issue. It is because hard domain and soft domain of an MLC STT-RAM cell cannot be flipped to the opposite magnetization direction at the same time. Thus, the soft domain has to be flipped twice to the opposite magnetization direction of the hard domain. The TT problem hurts the lifetime of MLC STT-RAM due to additional flips on soft domains. To mitigate the TT problem of MLC STT-RAM, we propose an alternative encoding scheme (AES) to reduce the occurrence of TTs. AES utilizes the encoding method to eliminate most TTs and distributes unavoidable TTs among cells evenly to improve the lifetime of MLC STT-RAM cache. The experimental results showed that the proposed scheme achieved a great lifetime improvement than the related work.