Molecular Electronic Sensors Modeling: From Theory to Applications

In the last twenty years, the impressive development of molecular electronics and its related technology made possible the establishment of molecular electronic sensors (MES). In particular, the advancements in molecular synthesis engineering and the evolution towards sub-photolithographic processes allowed to fabricate molecular sensors whose working principle is different from conventional molecular chemo-sensors. Indeed, in MES, the detection involves the electric current flow instead of other chemical-physical phenomena, thus making possible a direct integration with conventional electronic circuitry. Pollution, chemical compounds, humidity, temperature and light sensors are realizable by modulating the molecular channel conductivity, exploiting quantum phenomena such as intermolecular or photon interactions. The potential applications are many and varied: gas sensors for industrial processes or environment monitoring, e-noses for non-invasive disease diagnostics, wearable/implantable bio-sensors and single-molecule detection in chemical or biological processes. MES are promising for several reasons, among which: potentially high sensitivity, selectivity and detectability, huge integrability, fast response time, low cost, label-free detection. The first part of this work is a literature review of the theoretical physical-chemical modeling of MES. Molecular channel electronic structure, intermolecular interactions and transport state-of-the-art modeling techniques are introduced from the applicative standpoint of the electronic engineer, without requiring any extra notion w.r.t. the standard electrical/electronic engineering MSc background. To this purpose, the rigorous and purely quantum mechanical Non-Equilibrium Green's function (NEGF) theory is introduced, without the requirement of the second quantization formalism. The information provided in this part should be enough to perform an aware and correct setting up of atomistic simulations and to judiciously interpret the results. The second part is instead focused on developing a general and complete methodology for the design of a MES. This crucial point is still lacking in the literature, even if it should be the first step toward the engineering and industrialization of the design process. To this purpose, the C60 fullerene molecule is used as molecular channel, and the device-level design is performed suggesting a possible general methodology for the choice of the device optimal geometry and other device parameters. Then a complete characterization of the designed gas sensor is performed, analyzing the performances in terms of sensibility, selectivity and sensor response. This allows the potential development of a "black-box"-like model of the MES, to be used in designing the conditioning circuit, being also the starting point toward a design by levels of abstraction, analogously to what is well established in semiconductor companies.