Lowering of effective oxide thickness due to negative capacitance effects in polycrystalline ferroelectric HZO gate stacks

Hafnium Zirconium Oxide (HZO) superlattice heterostructures have emerged as a promising candidate for the gate stack of a ferroelectric field-effect-transistor. Recent work has experimentally demonstrated that a tetragonal/orthorhombic (t/o-) phase mixture with partially in-plane polarization can lead to energy landscape flattening and negative capacitance (NC) stabilization. However, there is a need for understanding the physical mechanisms of formation of domains and their dynamics to characterize the origin of NC effects in such gate stacks. In this work, we will present a 3D phase-field study to quantify the lowering of effective oxide thickness (EOT) in metal-ferroelectric-insulator-semiconductor heterostructures with realistic grain sizes. Our results show that the achievable EOT critically depends on the angle of the polar axis, the grain-size, t-phase fraction, and the density of domains.