Realizing ferroelectric Hf0.5Zr0.5O2 with elemental capping layers

Abstract

Hafnium zirconium oxide (Hf_0.5Zr_0.5O₂ or HZO) thin films show great promise for enabling ferroelectric field-effect transistors (FeFETs) for memory applications and negative capacitance FETs for low-power digital devices. One challenge in the integration of ferroelectric HZO is the need for specific capping layers to yield the most pronounced ferroelectric behavior; to date, superior HZO devices use titanium nitride or tantalum nitride, which limits HZO integration into various device structures. In this work, the authors demonstrate the use of elemental capping layers, including Pt, Ni, and Pd, for driving ferroelectricity in HZO. Different combinations of these capping metals, along with changes in the HZO thickness and annealing conditions, have yielded the optimal conditions for maximizing ferroelectric behavior. A remnant polarization of 19 μC/cm² and a coercive field strength of 1.07 MV/cm were achieved with the Pt/HZO/Ni stack annealed at 650 °C with a HZO thickness of ∼20 nm. These results bring even greater promise to the use of HZO in memory and/or digital electronic devices by expanding the toolkit of materials that may be used for realizing ferroelectricity.