Fault-tolerant multi-level logic decoder for nanoscale crossbar memory arrays

Abstract

Several technologies with sub-lithographic features are targeting the fabrication of crossbar memories in which the nanowire decoder is playing a major role. In this paper, we suggest a way to reduce the decoder size and keep it defect tolerant by using multiple threshold voltages (V T), which is enabled by our underlying technology. We define two types of multi-valued decoders and model the defects they undergo due to the V T variation. Multi-valued hot decoders yield better area saving than n-ary reflexive codes (NRC), and under severe conditions, NRC enables a non-vanishing part of the code space to recover. There are many combinations of decoder type and number of V T's yielding equal effective memory capacities. The optimal choice saves area up to 24%. We also show that the precision of the addressing voltages for decoders with unreliable V T's is a crucial parameter for the decoder design and permits large savings in memory area.