The Cold Source Field-Effect Transistor - Exploiting Ballistic Transport to Design a Low Subthreshold Swing Switching Device*

Power dissipations are to blame for part of the recent deceleration in the exponential growth rate of the transistor count on integrated circuits predicted by Moore's law. A relevant metric at the device level is the subthreshold swing (S) - the increment in gate voltage required for a tenfold increase in drain current - which is commensurate with energy losses during switching. For the ubiquitous Si Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), thermodynamics and electrostatics impose that S ≥ 60 mV/dec at room temperature. Phenomena beyond MOSFET physics thus need to be exploited to design a low S device; we show how ballistic transport can be used towards this end. In the resulting device, known as the cold source FET, thermionic emission is suppressed in the OFF-state by means of density-of-states engineering, thereby enabling low S while maintaining a high ON-state current. Deviations from the approximation of ballistic transport need to be considered for real-world implementations; we show how rethermalization due to inelastic scattering affects S.