Nonlinear Multi-Error Correction Codes for Reliable MLC nand Flash Memories

Abstract

Multi-level cell (MLC) nand flash memories are popular storage media because of their power efficiency and large storage density. Conventional reliable MLC nand flash memories based on BCH codes or Reed-Solomon (RS) codes have a large number of undetectable and miscorrected errors. Moreover, standard decoders for BCH and RS codes cannot be easily modified to correct errors beyond their error correcting capability t=[(d-1/2)], where d is the Hamming distance of the code. In this paper, we propose two general constructions of nonlinear multi-error correcting codes based on concatenations or generalized from Vasil'ev codes. The proposed constructions can generate nonlinear bit-error correcting or digit-error correcting codes with very few or even no errors undetected or miscorrected for all codewords. Moreover, codes generated by the generalized Vasil'ev construction can correct some errors with multiplicities larger than t without any extra overhead in area, latency, and power consumption compared to schemes where only errors with multiplicity up to t are corrected. The design of reliable MLC nand flash architectures can be based on the proposed nonlinear multi-error correcting codes. The reliability, area overhead and the penalty in latency and power consumption of the architectures based on the proposed codes are compared to architectures based on BCH codes and RS codes. The results show that using the proposed nonlinear error correcting codes for the protection of MLC nand flash memories can reduce the number of errors undetected or miscorrected for all codewords to be almost 0 at the cost of less than 20% increase in power and area compared to architectures based on BCH codes and RS codes.