A Review of Quantum-Dot Cellular Automata Based Adders

Quantum-Dot Cellular Automata (QCA) has been emerging as a new nanocomputing paradigm. QCA computing has many advantages like very high operating speed, extremely low energy dissipation, and very high device density. An adder is heart of arithmetic units of processors. So, many researchers have been working on design and implementation of reliable and robust QCA based adder circuit. This paper presents a comprehensive review of QCA based adder designs and implementations. Being an emerging future technology having potential of replacing CMOS technology, the paper comprehensively covers an introduction to QCA nanotechnology, QCA fundamentals, QCA technology developments, evolution of QCA adders, QCA full adder designs, performance metrics, and cost function computations for coplanar and multilayer QCA 1bit full adders. The QCA adder circuits reported by various researchers have been compared in terms of adder type (coplanar or multilayer), basic full adder structure type, type and number of majority gates used, number of inverters, number of wire-crossovers, delay, and number of QCA cells. Also, the cost functions have been computed for both coplanar and multilayer QCA adders by giving higher priority to complexity.