Readout system for molecular field-coupled nanocomputing based on a molecular junction

The field-coupled nanocomputing (FCN) is one of the most interesting beyond-CMOS technologies, in particular, its molecular implementation (molFCN) takes advantage of its intrinsic features: nanometric dimensions and low power requirement. With each passing year, it becomes increasingly important in electronics due to the slowdown in the scaling of traditional electronics. Until today, in the scientific literature, no integrated systems with molFCN and CMOS have been proposed. This thesis investigates the possibility of interfacing the CMOS technology with the FCN one. Three solutions have been thought of, which exploit different physical phenomena: capacitive coupling, photons scattering, and energy levels alteration. The system designed in this thesis is the molecular junction-based one. It is based on a nanogap made of gold (1,1,1) and Sulphur atoms were employed as anchoring groups. The molecules have been analyzed through the ORCA software to obtain the optimized geometry, the dipole moment parameter, and the polarizability values (the 3x3 tensor and the isotropic one). The results, in terms of polarizability and polarity, have been delivered on the QuantumATK environment, for building the molecular junction. The simulations performed through ORCA and QuantumATK are achieved with DFT accuracy. An ad hoc driver molecule has been designed to mimic the charge localization of molFCN in the ATK software, it is formed by a carbons chain with nitrogen at one side to provide the positive pole and oxygens on the other side to provide the negative pole. The goodness of the junction molecule is determined by the transmission spectrum and IV plot, but, for a deeper overview of the system quality, the orbitals and the conduction path in terms of angle and weight have been simulated. The IV plot is the most important result because it shows clearly the detection possibility of the binary value encoded in the molFCN; if the current difference between the two configurations is large enough, the system could distinguish the logic value. Orbital change provides direct proof of the driver's influence on the molecular junction, while conduction pathways contain the effective interaction between the atoms that compose the molecular junction and the traveling electrons. The results reveal the possibility of performing the readout using molecular junctions, in particular, the most conductive molecules exhibit a larger current difference between the two logic configurations. Two main molecule characteristics have been identified as crucial parameters, polarity and polarizability. The first one represents how much the dipoles inside the molecule orient themselves when an electric field is applied; while the second one provides asymmetry to the structure, therefore a different behavior depending on the configurations. The polar behavior is highlighted by the not-odd function represented in the IV plot, while the molecular junction based on the molecule with the highest polarizability values shows an odd graph in the trans-characteristic. For some molecules, additional analysis has been performed: the driver has been moved away from the initial position until double the initial distance and a smaller driver has been used; the simulations aimed to discover the robustness of the system to the fabrication tolerances and the not-perfect molecules positioning in realistic devices. This thesis places the basis for the research of readout systems able to adapt MolFCN structures to the standard CMOS technology.