Reliability and Performance Evaluation of QCA Devices With Rotation Cell Defect

As a novel nanotechnology, quantum-dot cellular automata (QCA) can achieve dense packages due to the extremely small size of quantum dots. However, fabrication defects and fault rates in the nanotechnology are expected to be quite high. In this paper, the behaviors of basic QCA devices in the presence of cell rotation are thoroughly analyzed in order to study their rotation defect tolerances and determine the ranges of allowable rotation angles. Rotation effect of QCA cell is modeled by using modified coherence vector formalism and rotation angle. The performances of five basic QCA devices with rotation cell defect are simulated under various cell sizes. The results show that different QCA devices have different rotation angle tolerances. The inverter is the weakest structure while the straight wire is the most reliable structure if measured by the smallest angle that impacts success rate, and the bigger cell size has a negative effect on allowable rotation angle range. More analysis results show that the diagonal cell and the cell close to the output perform the worst rotation tolerance on the inverter and the interconnect, respectively. Furthermore, the power gain of rotation defect device is discussed and the finding is provided that moderate rotation error can be restored at the location that is three cells away from the defect.