Strain fluctuations unlock ferroelectricity in wurtzites

Ferroelectrics are of interest for non-volatile data storage due to their reorientable, crystallographically defined polarization states, yet efforts to integrate perovskites into ultrathin memories have been frustrated by film-thickness scaling constraints, limiting ferroelectric switching under low voltage. Wurtzites [1], including magnesium-substituted zinc oxide [(Zn,Mg)O] [2], have recently been shown to exhibit scalable ferroelectricity. While first-principles calculations suggest that a biaxial tension of a few percent promotes ferroelectricity in wurtzites [3,4], biaxial strains are found to not exceed 0.3% in (Zn,Mg)O at the solubility limit of Mg in bulk ZnO. In this work, we explain the observations of ferroelectricity in (Zn,Mg)O by examining the influence of Mg substitution on interatomic bonding and ferroelectric switching. We demonstrate that large strain fluctuations emerge locally around Zn and Mg cations in (Zn,Mg)O, causing a reduction of up to 45% in the local coercive fields via sequential polarization reversal. This work opens up an avenue to develop scalable ferroelectrics for ultrathin microelectronics.

[1] Calderon et al. Science 380, 1034-1038 (2023).

[2] Ferri et al. J. of Appl. Phys. 130, 044101 (2021).

[3] Konishi et al. Appl. Phys. Lett. 109, 102903 (2016).

[4] Moriwake et al. Appl. Phys. Lett. 104, 242909 (2014).