Robustness analysis and enhancement strategies for quantum-dot cellular automata structures

Abstract

QCA (Quantum-dot Cellular Automata) has been pointed out as a candidate for CMOS (Complementary Metal-Oxide Semiconductor) succession. The transmission and processing of information in QCA circuits occurs without flow of electrons, resulting in tremendouslylow power consumption. Furthermore, the design of QCA circuits generally requires less area than its CMOS counterpart and high clock frequencies are supposed to be achieved. Despite its many advantages in comparison to CMOS, QCA has to overcome several challenges, most of them related to its physical implementation and robustness. Thus, thecreation of robust QCA structures as well as methodologies for error analysis for QCA are mandatory steps to the consolidation of this emerging nanotechnology. This work introduces a QCA Defects Simulator that employs a novel methodology for errors analysis in QCA structures. Such errors may occur at output signals due to eitherstructural defects into the cells or unexpected shifts in the clock signals. The tool provides a quantitative measure of the robustness level of the structure, named error-free simulations rate. Moreover, it produces a heat map by which it is possible to identify the weakest polarization points when the structure is submitted to structural defects testing undercertain classes of defects. After the weak polarization points in structures are identified by means of the heat maps, they undergo an addition of cells and strategical structural changes in order to create modified robustness enhanced structures. Then, the performance of the modified structures are compared to their regular counterparts. Results of the tests performed demonstrated the superior robustness of the modified fundamental components under combined classes of defects. Moreover, a slightly robustness enhancement was achieved when the modifiedfundamental components were used to replace their regular counterparts within more complex QCA circuits and systems. Regarding to the robustness enhancement of phase-shifted QCA clock signals, an asynchronous clock strategy is proposed as an alternative to the traditional synchronous clock. The clock shifts testing at QCA Defects simulator was used to generate random shifts in the clock signals, allowing the comparison of the error-free rates for both synchronous andasynchronous clock signals strategies. The results for tests performed with fundamental components showed an increasing in the error-free simulations rate for shifts within the range of 0 to /4 radians.