A Low-Complexity Endurance Modulation for Flash Memory

The repeated program/erase (P/E) cycles wear out flash memory cells which limits the device's lifetime. The larger the injected/erased charge, the faster the wear out rate and thus there is interest in reducing the percentage of cells programmed to high voltage levels. Conventional data shaping techniques often introduce a nonnegligible overhead as well as incurring additional complexity to encode the input data into shaped codewords and decode the read data. We propose a novel lossless yet simple endurance modulation technique that relies solely on the error-correction code (ECC) to retrieve the original data. This idea is motivated by the fact that ECCs are usually designed to correct channel errors towards the end of the device's lifetime and hence at early age, the ECC can be jointly used for channel error correction and endurance demodulation. The proposed scheme consists of data shaping by flipping bits in a controlled manner and simple max-log demodulation to recover those flipped bits. The simulation results show that the proposed scheme does not undermine the device's ability to recover the original data if the shaping gain is adjusted as the device ages. Once the channel errors exceed a prescribed threshold, the controller disables the endurance modulation and operates in normal mode.