novel defect terminolgy beside evaluation and design fault tolerant logic gates in quantum-dot cellular automata

quantum dot cellular automata (qca) is one of the important nano-level technologies for implementation of both combinational and sequential systems. qca have the potential to achieve low power dissipation and operate high speed at thz frequencies. however large probability of occurrence fabrication defects in qca, is a fundamental challenge to use this emerging technology. because of these various defects, it is necessary to obtain exhaustive recognition about these defects. in this paper a complete survey of different qca faults are presented first. then some techniques to improve fault tolerance in qca circuits explained. the effects of missing cell as an important fault on xor gate that is one of important basic building block in qca technology is then discussed by exhaustive simulations. improvement technique is then applied to these xor structures and then structures are resimulated to measure their fault tolerance improvement due to using these fault tolerance technique. the result show that different qca xor gates have different sensitivity against this fault. after using improvement technique, the tolerance of xor gates have been increased, furthermore in terms of sensitivity against this defect xors show similar behavior that indicate the effectiveness of improvement have been made.