Alternative explanation for the steep subthreshold slope in Ferroelectric FETs.

Since many years, sub-60mV/decade switching has been reported in ferroelectric FETs. However, thus far these reports have lacked full physical explanation since they typically use a negative capacitance in the ferroelectric layer to be able to explain the experimental observations. Because negative capacitance as such is not a physical concept, we propose an alternative model that relies on the non-linear and non-equilibrium behavior of the ferroelectric layer. It is shown that a steep subthreshold slope can be obtained by a 2-step switching process, referred to as nucleation and propagation. Making use of the concept of domain wall motion as known also from fracture dynamics, we are able to explain the steep slope effect. A simple mathematical model is added to further describe this phenomenon, and to further investigate its eventual benefit for obtaining steep slope transistors in the sub-10nm era.