VHDL-AMS implementation of a numerical ballistic CNT model for logic circuit simulation

This paper introduces a novel numerical carbon nanotube transistor (CNT) modelling approach which brings in a flexible and efficient cubic spline non-linear approximation of the non-equilibrium mobile charge density. The spline algorithm creates a rapid and accurate solution of the numerical relationship between the charge density and the self-consistent voltage, which leads to the speed-up of deriving the current through the channel without losing much accuracy. This modelling method also allows the flexibility of choosing different cubic spline intervals which may affect the performance of the model, but it is still capable of obtaining an acceleration of more than a 100 times while maintaining the accuracy within less than 1.5% normalised RMS error compared with previous reported theoretical modelling approach. The model has been proved working as transistors in a logic inverter implemented using VHDL-AMS and simulated in SystemVision, which shows the availability of implementing a circuit-level simulators with our proposed model. Additionally, although this model is originally based on the ideal ballistic transport characteristics, it shows good flexibility that the extension with numbers of non-ballistic features are certainly acceptable.