Quantum-dot cellular automata (QCA) is a very interesting nanoscale technology. Ultradense structure and ultralow power consumption are the most important features of QCA compared to CMOS. QCA circuits often suffer from various types of manufacturing defects and are therefore prone to fault. Hence, the design of fault-tolerant circuits in QCA technology is considered a necessity. In this paper, a novel fault-tolerant three-input majority gate is presented using 12 simple and rotated cells in QCA technology. The proposed structure is investigated against all kinds of cell omission, extra-cell deposition, and cell displacement defects. The simulation results are verified by QCADesigner 2.0.3, and it showed 100%, 89.29%, and 100% tolerance against single-cell omission, double-cell omission, and extra-cell deposition, respectively. In addition, the proposed structure is robust against cell displacement defects. Finally, using the proposed structure, a novel coplanar full adder is presented. The results were compared and indicated that the proposed designs are more reliable than the existing designs. Furthermore, QCAPro power estimator tool was employed to estimate the energy dissipation of the proposed structure.
KEYWORDSfault-tolerant, nanotechnology, quantum-dot cellular automata (QCA), three-input majority gate
INTRODUCTIONIn the near future, complementary metal-oxide-semiconductor (CMOS) technology is expected to reach the end of its way due to limitations such as switching speed, scaling specifications, high cost of lithography, and thermal challenges. 1-3 CMOS technology also suffers from lower tolerability and manufacturing diversity, which have a negative impact on the reliability of these devices, leading to an increase in the number of faults. Future CMOS constraints have led many researchers to design nanoscale devices. 4 Quantum-dot cellular automata (QCA) has appeared as a favorable new innovation for future integrated circuit generation, which can overcome CMOS constraints. 3 The simplest element in QCA technology is a square cell with four quantum dots located in its four corners. The transfer of information takes place by columbic interactions between the fundamental elements (cells) instead of electrical current. [3][4][5] Up to now, extensive attempts have been made on the design of various digital circuits such as multipliers, 6-8 adders, 9-19 memory devices, 20-23 arithmetic and logic unit, 24 and multiplexers [25][26][27][28][29] in QCA technology, but according to a conducted study by Bahar et al, 30 the high complexity of nanocircuit structures results in the need to design high fault-tolerant structures. The QCA technology encounters with a variety of manufacturing defects such as extra-cell deposition, cell omission, cell displacement, or cell misalignment that make QCA circuits unusable. 31,32 A three-input majority gate is considered one of the main basic gate in the QCA circuits. 33,34 Providing robust structures for the majority gate will result in the creation of fault-tolerant logic cir...