The film thickness dependence of ferroelectric Si:HfO₂ (10 nm and 30 nm) was studied with a focus on ferroelectric field effect transistor (FeFET) memory applications based on a 28 nm bulk technology. Experimental P-E hysteresis of metal-ferroelectric-metal capacitor structures could be reproduced by a Preisach-based ferroelectric simulation model implemented in a commercially available TCAD environment. The experimentally observed thickness dependence of material characteristics was then used for demonstrating memory window widening, reduced interfacial field stress and decreased depolarization fields by FeFET TCAD modeling. Based on these findings, improved memory characteristics (memory window size, endurance, retention) can be anticipated for FeFET devices possessing the appropriate Si:HfO₂ thickness.