Polar Codes for Spin-Torque Transfer Magnetic Random Access Memory

Abstract

Spin-torque transfer magnetic random access memory (STT-MRAM) is a promising non-volatile memory (NVM) technology due to its superior performance in terms of power consumption, write/read speed, endurance, and scalability. However, the reliability of STT-MRAM is affected by the process variation and thermal fluctuation, leading to both the write errors and read errors. Hence, it is important to develop error correction coding schemes to correct the memory cell errors and improve the system reliability. In this paper, we propose, for the first time, the design and optimization of polar codes for the STT-MRAM channel. In particular, as the STT-MRAM channel is asymmetric by nature, we first adopt an approach to symmetrize the channel so as to facilitate the design of effective polar codes. We then apply the density evolution method to construct polar codes and optimize their performance for the STT-MRAM channel. Furthermore, in order to mitigate the raw bit error rate diversity of STT-MRAM cells caused by process variations, we propose a rate-adaptive polar coding scheme in conjunction with an adaptive decoding algorithm. Simulation results and the decoder complexity analysis show that the constructed polar codes outperform both the Bose–Chaudhuri–Hoquenghem codes and low-density parity-check codes with lower decoding complexity, thus demonstrating the great potential of polar codes for improving the reliability of emerging NVMs.