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Fault Secure Encoder and Decoder for NanoMemory Applications

Helia Naeimi and André DeHon
IEEE Transactions on Very Large Scale Integration (VLSI) Systems , Volume 17, Number 4, Pages 473--486, April, 2009.

Memory cells have been protected from soft errors for more than a decade; due to the increase in soft error rate in logic circuits, the encoder and decoder circuitry around the memory blocks have become susceptible to soft errors as well and must also be protected. We introduce a new approach to design Fault-Secure encoder and decoder circuitry for memory designs. The key novel contribution of this paper is identifying and defining a new class of Error-Correcting Codes whose redundancy makes the design of Fault-Secure Detectors (FSD) particularly simple. We further quantify the importance of protecting encoder and decoder circuitry against transient errors, illustrating a scenario where the system failure rate (FIT) is dominated by the failure rate of the encoder and decoder. We prove that Euclidean Geometry Low-Density Parity-Check (EG-LDPC) codes have the Fault-Secure Detector capability. Using some of the smaller EG-LDPC codes we can tolerate bit or nanowire defect rates of 10% and fault rates of 10-18 upsets/device/cycle, achieving a FIT rate at or below one for the entire memory system and a memory density of 1011 bits/cm2 with nanowire pitch of 10nm for memory blocks of 10Mbits or larger. Larger EG-LDPC codes can achieve even higher reliability and lower area overhead.

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