Steep Subthreshold Swing Originating from Gate Delay

Complex gate dielectrics are being widely explored to provide voltage amplification leading to steep subthreshold swing (SS) in transistors [1]. Here we show that hysteretic steep SS can arise simply from the introduction of a series resistance in the gate of a metal-oxide-semiconductor field-effect transistor (MOSFET), i.e. as a dynamic effect. The choice of measurement slew rate (SR) and slew direction then directly affects the measured SS as has been previously reported [2]. We use an ionic polymer gate dielectric to illustrate how in this case the series resistance arises from the ionic conductance, which controls the time response of the electric double layer (EDL) at the polymer/metal [3] or polymer/semiconductor interface [4]. While the ionic polymer in an EDL transistor is used to illustrate the effects, the principles apply generally to other complex insulating gates including ferroelectrics and piezoelectrics.