Elucidating possible crystallographic origins of wake-up mechanisms in ferroelectric hafnia

Abstract

The wake-up in doped hafnia ferroelectric devices is an extremely important process to understand in order to integrate these materials successfully into working ferroelectric memory devices. The crystallographic origins of this process are clarified with three main mechanisms. Strain relaxation in the ferroelectric orthorhombic phase led to an adjustment of the unit cell volume toward a "bulk-like" value. The undistorted cell allowed for easier polarizability within the unit cell, allowing higher polarization. Reversible phase transformations between the tetragonal and orthorhombic phases depend on the nature of the strain. Finally, a model is developed describing grain reorientation, inducing a 90 degrees rotation of the orthorhombic unit cell and allowing the phase to respond to the E-field more readily under cycling.