Fig. 1: Structural and ferroelectric properties of ultrathin epitaxial HZO films.

A HZO polymorph phases with their preferred orientations. The projection direction is perpendicular to the preferred planes. B XRD patterns of 1-, 3-, and 5-nm-thick HZO epitaxial films grown on (100) STO substrates buffered with LSMO layers. C Switchable polarization of 5-nm-thick HZO epitaxial films evaluated by PUND measurements. The 2Pr values plotted are corrected for the leakage current contribution obtained by analyzing charge profiles of the PUND measurements. Details of the 2Pr value evaluation are provided in Supplementary Materials. The error bars indicate variations in the polarization values obtained by ten repeated measurements. D External d.c. bias dependence of off-field PFM phase and amplitude for the 1-nm-thick epitaxial HZO thin films. E Box-in-box domain writing for 1-nm-thick HZO epitaxial films with poling bias of ±2 V. The scale bar denotes 500 nm.