We present analytical models and numerical simulations addressing the fundamental limits to the sub-threshold swing (SS) in Dirac-Source FETs (DS-FETs), based on either graphene or 3D Dirac semimetals. To this purpose, we devised and implemented a semi-analytical model for DS-FETs employing a 3D Dirac source. Numerical results confirm analytical predictions. Our findings help to clarify the physics behind the minimum SS in DS-FETs, and the possible advantages offered by 3D Dirac semimetals.
