Impact of total and partial dipole switching on the switching slope of gate-last negative capacitance FETs with ferroelectric hafnium zirconium oxide gate stack

We report, for the first time, a gate last process, used to fabricate Negative Capacitance field effect transistors (NCFETs) with Hf0.5Zr0.5O2 (HZO) as ferroelectric (FE) dielectric in a metal/ferroelectric/insulator/semiconductor (MFIS) configuration. Long channel NCFET's with HZO thickness down to 5 nm exhibit consistent switching behavior with switching slope (SSrev) below kT/q over four decades of drain current. Temperature dependent transport study shows that, the effective mobility of HZO NCFETs is 15 % higher than that of HfO2 based control MOSFETs due to suppression of Hf diffusion into the interfacial SiO2 layer (IL). Using the Preisach hysteresis model, which models dynamics of FE switching through a cluster of independent switching dipoles at arbitrary electric field, we (a) explain the asymmetric SS behavior of NCFETs in MFIS configuration, and (b) establish design guidelines for achieving sub-kT/q SS in both forward and reverse sweep direction.