Miha Janež (2012) Methods for placement and routing of quantum-dot cellular automata logic gates. PhD thesis.
Due to continuous development, the miniaturization of the integrated circuits in CMOS technology is approaching its limit. Thus emerged several proposals for new technologies that would take advantage of the effects which hinder the operation of miniaturized CMOS circuits. One of the proposed novel technologies is the quantum-dot cellular automaton (QCA). Its basic building block is a QCA cell with four quantum dots and two electrons which can assume two configurations within a cell. Electrostatic effects enable the transfer of data between cells. Therefore, the QCA can perform binary processing. Researchers constructed various logic gates composed of QCA cells, including the majority gate, the inverter and the wire. This enables the construction of complex QCA structures. As in the design of CMOS circuits, the QCA design methodology must be formalized and computer aided design must be introduced. In this thesis we address the automatization of the layout design of QCA structures. Layout design consists of placement and routing of logic gates. We developed the methods for automatic placement and routing of QCA logic gates, thus introducing the computer aided design of QCA structures. We analyzed existing algorithms for layout design in CMOS technology and adapted them for layout design of QCA structures. For placement of QCA logic gates we used the simulated annealing algorithm. For routing of placed gates we developed the algorithm based on the maze router and the line probe search. Correctly operating structures can be designed only by using the design rules that determine the necessary structure characteristics. Thus, the design rules must be considered by the computer tool for automatic QCA layout design. In thesis we defined the design rules that must be satisfied by correctly operating structure. The defined design rules take into account the physical characteristics of QCA, thus their use enables the design of manufacturable structures. In order to evaluate the characteristics of automatically designed QCA structures we defined appropriate metrics. They were used to assess the quality of automatically designed structures. Based on the introduced metrics we compared automatically designed and manually designed QCA structures. We implemented the computer tool for automatic layout design of QCA structures. We used the tool to design several QCA structures and we analyzed the results. Correct operation of all designed structures was verified by the simulation in QCADesigner tool.
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