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.