Thermal Stability of Ferroelectricity in Hafnia-Zirconia-Alumina Buried Oxide Stacks

The thermal stability of 20 nm buried oxide (BOX) with ferroelectric (Fe) stacks grown by pblasma enhanced atomic layer deposition (PEALD) was investigated in bonded silicon-on-insulator (SOI) structures after the RTA treatment at 600-1000 °C for using them in silicon-ferroelectric-silicon (SFS) optical switches or FeFET memories. Various stacks had different ferroelectric thermal stabilities, where the highest residual polarization P
r
= 5.5 µC/cm
²
was demonstrated for HfO
2
:Al
2
O
3
(10:1) deposited monolayer stacks and annealed up to 900 °C.