Molecular transistor circuits: From device model to circuit simulation

Molecular devices have been proposed as an alternative solution for the design and fabrication of complex logic functions. In this paper a hybrid model of the molecular transistor (MT) is used to simulate different logic circuits. The model is based on the density function theory (DFT) combined with the Non Equilibrium Greens Function (NEGF) to find the transmission spectrum (TS) at equilibrium. The self-consistent method is used to calculate the I-V characteristics at nonequilibrium condition, considering the more realistic case of broadening of energy levels under the assumption of strong molecule electrode coupling. We have used a four terminal device with source, drain and two gate electrodes: one (backgate) used to increase the I_ON/I_OFF ratio and the other as normal control gate. The very same device is contextualized in the case of a structure feasible with currently available technology and several technological parameters are used to explore the solution space. This ensemble has been described and simulated using VHDL-AMS and allowed the design of a library of logic cells e.g NAND, NOR, Inverter and Half Adder suitable for architecture design. Results are given on both the modeling level and the circuits functional performance. Our findings represent an important breakthrough in the state of the art 1) for the methodology and design flow used and 2) for the detailed understanding on the device analyzed and optimized with the point of view of the circuit designer.