Study of clocking system for molecular FCN

In the last decades, to obtain increasingly high-performance devices, both in sense of frequency and density of logic elements in a single chip, a continuous scaling of electronic technology has been performed following Moore's law. Nowadays it is quite physically impossible to continue the scaling using a standard structure based on metal oxide and semiconductor due to atomic scale size. For this reason, some alternatives must be found in order to continue with the technological progress. In the last decade, the concept of Beyond-CMOS was born. It refers to the discovery and the development of new technologies, no more CMOS based, that can overcome the mentioned problems. Field-Coupled Nanocomputing devices are among the most promising ones: the computation is performed without a current flow or exploiting voltage levels but via local interactions among single entities; the power consumption can be drastically reduced. This group of devices includes Quantum-dot Cellular Automata logic. They can be implemented using nanomagnets, metallic junctions, semiconductors, and molecules. The latter called Molecular Quantum Cellular Automata are the most promising and have been studied in this thesis. In Molecular QCA the information is encoded in the charge distribution of oxidized molecules; in particular, the charge is aggregated in two redox center called quantum dots, and it can pass from one dot to another one without leaving the molecule. The basic cell is so formed by two near molecules and the four dots are placed as in the corners of a square. In this way only two possible con gurations can be obtained one that is associated to the logic state '0' and one associated to '1' due to the fact that the charge tends to move in order to minimize the total energy. By arranging mQCA cells in speci ed layouts anchoring the molecules on a gold substrate, many devices can be implemented: binary wire, majority voter and the inverter. Bis-ferrocene molecules have been synthesized ad hoc for QCA purposes; 3 dots in which the charge can be localized are present. If the molecule is subjected to an electric eld vertically oriented downwards the charge is locked in dot 3 and the molecule is in 'NULL' state; on the contrary with an electric led vertically oriented upwards the charge is free to move in dot 1 and dot 2. So changing the sign of the electric eld the molecule can be activated or inhibited. The electric eld is generated by some electrodes positioned in such a way that inside the trench it can be considered always vertically oriented. Whatever structure, even the simplest, required a clock system that controls and coordinates the propagation of the in- formation. The idea is to divide the circuit into different clock zones, each of them subject to a different value of electric eld. Ideally, the electrodes influence only the molecules of the corresponding clock zone and these ones are subject to the same value of electric eld. Until now only this ideal case has been studied. In reality, this is not true, indeed the clock zones are not sharply separated and each molecule is submitted to a different value of electric eld. The result is that the molecules anchored close to the next or previous clock zone show an intermediate behavior because they are not completely switched on or off. In this work, the binary wire, the majority voter and the T structure have been analyzed, considering the real values of the electric field.