The low resistive band-to-band tunnelling (BTBT) model has been developed for radio-frequency (RF) silicon negative differential resistance (NDR) device simulation on the TCAD platform. The BTBT mechanism in a forward-biased tunnel junction is modelled based on a generation-recombination term in a continuity equation by considering a spatially varying electric field through the tunnelling distance. Using this model, DC/AC characteristics of silicon NDR devices have been successfully described on a numerical device simulation platform. The calculated speed index from the junction capacitance and peak tunnelling current of the tunnel diode shows good agreement with experiments.