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 Hf
_0.5
Zr
_0.5
O
₂
(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 (SS
_rev
) 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 HfO
₂
based control MOSFETs due to suppression of Hf diffusion into the interfacial SiO
₂
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.