Towards Non-Volatile Spin Orbit Devices: Deposition of Ferroelectric Hafnia on Monolayer Graphene/Co/HM Stacks

TL;DR

This study demonstrates the successful atomic layer deposition of ferroelectric Hf0.5Zr0.5O2 on graphene/Co/heavy metal stacks, preserving magnetic and structural properties, and enabling potential non-volatile spintronic memory devices.

Contribution

It introduces effective nucleation methods for ferroelectric HZO on complex stacks, maintaining magnetic and structural integrity for spintronics applications.

Findings

HZO exhibits remanent polarization up to 19.2 μC/cm² with in-situ nucleation.

Stack maintains strong perpendicular magnetic anisotropy after HZO deposition.

High-quality interfaces remain unperturbed by ferroelectric deposition and annealing.

Abstract

Although technologically challenging, the integration of ferroelectric thin films with graphene spintronics potentially allows the realization of highly efficient, electrically tuneable, non-volatile memories. Here, the atomic layer deposition (ALD) of ferroelectric Hf$_{0.5}$Zr$_{0.5}$O$_2$ (HZO) directly on graphene (Gr)/Co/heavy metal (HM) epitaxial stacks is investigated via the implementation of several nucleation methods. With an in-situ method employing an Al$_2$O$_3$ layer, the HZO demonstrates a remanent polarization (2Pr) of 19.2 $\mu C/cm^2$. An ex-situ, naturally oxidized sputtered Ta layer for nucleation produces a film with 2Pr of 10.81 $\mu C/cm^2$, but a lower coercive field over the stack and switching enduring over subsequent cycles. Magnetic hysteresis measurements taken before and after ALD deposition show strong perpendicular magnetic anisotropy (PMA), with only slight deviations in the magnetic coercive fields due to the HZO deposition process, thus pointing to a good preservation of the single-layer Gr. X-ray diffraction measurements further confirm that the high-quality interfaces demonstrated in the stack remain unperturbed by the ferroelectric deposition and anneal.