An ECC-Based Repair Approach with an Offset-Repair CAM for Mitigating the MBUs Affecting Repair CAM

Abstract

Memory system reliability is a serious concern in many systems today and is becoming more worrisome as technology scales, system size grows and the demand of aggressive voltage reduction becomes more stringent. Thus, disposing of memory repair architectures with strong fault tolerance capability at low cost is desirable. In this context, Error Correcting Codes (ECC)-based repair techniques were proposed and offer aggressive reduction of the repair cost for high defect densities. However, an important issue in advanced process nodes is the fact that, single particles induce Single-Event Upsets (SEUs) in neighbor memory cells, thus leading to Multi-Cell Upsets (MCUs) and Multi-Bit Upsets (MBUs), when they occur in the same memory word. In the case of memories, there exist efficient approaches mitigating this kind of MBUs, in particular the use of interleaving. But when a memory is repaired, the impact of MBUs on the circuitry repairing the faulty memory words should also be mitigated. This can be done by using a repair Content Addressable Memory (CAM) having interleaving at its data-words, or else an Offset CAM. In this paper we present and evaluate a novel repair approach that uses the Offset CAM in ECC-based Memory Repair and hence permits the mitigation of the MBUs affecting it.