Defect tolerance in QCA-based PLAs

Defect tolerance will be critical in any system with nano-scale feature sizes. This paper examines some fundamental aspects of defect tolerance for a reconfigurable system based on magnetic quantum-dot cellular automata (MQCA). MQCA performs logical operations and moves data by manipulating the polarizations of nano-scale magnets, has been experimentally demonstrated, and operates at room temperature. We consider how specific defects will impact device functionality. Within this context, we introduce techniques for mapping Boolean logic functions to a defective system architecture (a reconfigurable programmable logic array design for MQCA). Simulation results show that our new mapping techniques can achieve much higher yields than existing techniques for nanowire crossbar PLAs.

I. Introduction

At present, there are a number of research efforts that have focused on different devices that might either replace or augment CMOS technology such that the performance scaling trends that we have seen for the last 30 years – and expect to see for the next 10–15 years – might continue beyond the year 2020. The work presented here looks at the Quantum-dot Cellular Automata (QCA) device architecture – and more specifically a reconfigurable, systems-level architecture realized with a magnetic implementation of QCA devices. This work is based on the work in [12] and [5], but represents two important steps toward a realistic, computationally interesting system. First, we show via physical-level simulation what logical faults we can expect in a physically-realized QCA-based circuit. We consider how these faults will affect the functionality of a reconfigurable PLA and propose mapping techniques to improve overall yield.