Subthreshold Behavior of Floating-Gate MOSFETs With Ferroelectric Capacitors

The subthreshold behavior of floating-gate MOSFETs connected with ferroelectric capacitors (FeCs) was investigated experimentally and theoretically. We found that the subthreshold swing (SS) decreases with decreasing ferroelectric capacitance (i.e., with the decreasing FeC area), in contrast to the voltage dividing effect of regular dielectric capacitors. The ferroelectric polarization switching counteracts the effect of voltage dividing by introducing an additional charge onto the floating gate, which improves the SS and leads to the observed SS dependence. The SS improvement caused by the polarization switching is different from the negative capacitance effect, which is helpful to further understand the ferroelectric transistor.