On Improving Fault Tolerance of Memristor Crossbar Based Neural Network Designs by Target Sparsifying

摘要

Memristor based crossbar (MBC) can execute neural network computations in an extremely energy efficient manner. However, stuck-at faults make memristors cannot represent network weight correctly, thus degrading classification accuracy of the network deployed on the MBC significantly. By carefully analyzing all the possible fault combinations in a pair of differential crossbars, we found that most of the stuck-at faults can be accommodated perfectly by mapping a zero value weight onto the memristors. Based on such observation, in this paper we propose a target sparsifying based fault tolerant scheme for the MBC which executes neural network applications. We first exploit a heuristic algorithm to map weight matrix onto the MBC, aiming at minimizing weight variations in the presence of stuck-at faults. After that, some weights mapped onto the faulty memristors which still have large variations will be purposefully forced to zero value. Network retraining is then performed to recover classification accuracy. For a 4-layer CNN designed for MNIST digit recognition, experimental results demonstrate that our scheme can achieve almost no accuracy loss when 10% of memristors in the MBC are faulty. As the faulty memristors increasing to 20%, accuracy loss is only within 3%.