Molecular FET: From Device Modeling to Circuit Design and Simulation

Molecular devices can play an important role in emerging future nanoelectronics with advantages in terms of functional density and integration. Recently, molecular electronics has gained a great interest from both theoretical and applied electronics point of view. The research has focused on the better understanding of basic transport properties of these devices. A lot of work has been going on in the development of designs based on molecular devices. the analysis of molecular structures involving the integration of many transistors is limited by the lack of an accurate and computationally efficient model. Thus, it is necessary to develop models and methods to enable the design with optimal trade-offs between the accuracy to describe quantum physics phenomena and the complexity to design and simulate circuits. Our research is aimed at developing an accurate and computationally efficient model to calculate the electron transport characteristics of the molecular transistor. In order to achieve this goal, a behavioral characterization was performed by varying the type of molecules, their lengths and the terminal groups and analyzed different factors that affect the electronic conduction of molecular systems. Moreover, the effect of gate voltage was observed which controls the electronic current by modulating the energies of molecular orbitals. Based on aforementioned observations, a model was derived that efficiently imitates I-V characteristics of molecular transistor by minimizing the detailed chemical and physical computational over-head. The computational cost and accuracy of the proposed model has been analyzed by comparing it with the atomistic simulation as a reference. The results show a remarkable improvement in terms of computational time. The simulation time is reduced six order of magnitude while maintaining the accuracy. The model is then integrated with hardware descriptive language to show its functional viability at circuit level simulation by implementing different logics like NAND, NOR, OR and some complex structures like Pentium 4 adder in crossbar like architecture. The non linear behaviour, impact of strong metal-molecule coupling and the use of back-gate in molecular devices are demonstrated to show their effects on the circuit level simulation. We develop a new modular framework based on VHDL-AMS that allows a comparison among different Molecular-FET models in terms of capability to capture an accurate I-V characteristics. It also allows to analyze the impact of Molecular-FET and to inspect the circuit proper behavior and its possible use in an architecture organized as a cascade of basic crossbars.