Defect characterization and tolerance of QCA sequential devices and circuits

This paper analyzes the defect tolerance of sequential devices and circuits implemented by molecular quantum-dot cellular automata (QCA). Initially, a novel QCA SR-type flip-flop is proposed; this flip-flop is the first sequential device for QCA and it takes into account the timing issues associated with the adiabatic switching of this technology. Using a defect model by which single additional and missing cells are considered in a molecular implementation, simulation results are provided for a logic-level characterization of the defects. Also for sequential circuits, defect tolerance is pursued and shown to affect the functionality of basic QCA devices, resulting mostly in unwanted inversion and stuck-at faulty behavior at logic level.