Lowering Effective Dielectric Constant of Ferroelectric Hf0.5Zr0.5O2 Film with an Ultra-Thin Al2O3 Intermediae Layer

Abstract

HfO2-based thin films have been one of the most active research topics in recent years due to their various advantages, including high dielectric constant and robust ferroelectricity. However, in the gate stack of metal-ferroelectric-insulator-silicon (MFIS), the much larger dielectric constant of HfO2-based ferroelectric layer compared with the insulating layer leads to insufficient voltage drop across the ferroelectric layer, necessitating a higher voltage to induce the electric field required for reversing the polarization direction. To resolve this issue, a HfO2-based thin film with reduced dielectric constant is highly preferential. In this study, we demonstrate an experimental method for reducing the dielectric constant of HfO2-based thin film while maintaining its robust ferroelectric properties. The key idea is to incorporate a thin Al2O3 intermediate layer within a Hf0.5Zr0.5O2(HZO) ferroelectric layer to form a tri-layer structure (HZO/Al2O3/HZO) with precisely controlled thicknesses by using atomic layer deposition(ALD). Additionally, we investigate how the processing conditions of sputtered TiN layers affect the ferroelectric and dielectric properties of the tri-layer structure and a single-layer HZO grown on it.