Demonstration of Low EOT Gate Stack and Record Transconductance on $L_{\mathrm{g}}=90$ nm nFETs Using 1.8 nm Ferroic HfO2-ZrO2 Superlattice

We report significantly enhanced gate capacitance
$(C_{\text{gg}})$
in 1.8-nm HfO
2
-ZrO2 superlattice (HZH) gate stack on n-MOSFETs, enabled by the ferroic nature of the constituent layers. The HZH gate stack exhibits co-existence of both ferroelectric and antiferroelectric phases, a unique mixed order, that has never been reported for films with such a low thickness [1]. Gate stacks combining this superlattice with an un-scavenged SiO
2
interlayer (IL) (~8 Å), show a combined effective oxide thickness (EOT) of 7.5 Å on both bulk and SOI n-MOSFETs. This represents over 2-Å lowering of the EOT compared to Hf0
2
control produced using identical process conditions. Importantly, the enhanced
$C_{\text{gg}}$
shows no frequency dispersion up to 25 GHz. Since no IL scavenging is employed, the electron mobility and injection velocity are unaffected. Aided by a lower EOT, a record-high intrinsic transconductance of 1.5
$\text{mS}/\mu \mathrm{m}$
is demonstrated in 90-nm SOI n-MOSFETs with the HZH gate stack, together with a 14% increase in ON-current relative to the Hf0
2
control.