Physical Model for the Steep Subthreshold Slope in Ferroelectric FETs

Since many years, sub-60 mV/decade switching has been reported in ferroelectric FETs. However, thus far these reports have lacked full physical explanation since they often use a negative capacitance model 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 explained by a 2-step switching process, referred to as nucleation and domain growth. Making use of the concept of domain growth, we can explain the steep slope effect. A simple mathematical model is added to further describe this phenomenon, and to investigate its eventual benefit for obtaining steep slope transistors in the sub-10 nm era.