First Demonstration of High Remanent Polarisation in 10 nm Polycrystalline BaTiO₃ Films

In recent years, the possibility to grow high-quality ultrathin ferroelectric films has revived interest in perovskite ferroelectrics for FeRAM applications, which were once believed to have reached their scaling limits. In these devices, the ferroelectric is sandwiched between two conductive electrodes and the information is stored by the polarisation direction in the ferroelectric film [1]. The high remanent polarisation and low coercive field of perovskites make them ideal ferroelectric materials for low-power memory applications. Ferroelectricity has been observed in ultrathin perovskite films down to 5 nm in epitaxy [2,3,4] but has yet to be demonstrated in polycrystalline films, which are preferred in production due to the placement of capacitors in the back-end-of-line for DRAM-like technologies.<br/>In this work, the thickness scaling of polycrystalline BaTiO₃ down to 10 nm is demonstrated with remarkable remanent polarisation values. This work was enabled by the development of a novel platinum silicide based conductive electrode that also acts as an oxygen migration barrier at the high temperatures required for growth of BaTiO₃. This bottom electrode was used as a template to deposit LaNiO₃(perovskite bottom electrode) followed by BaTiO₃ thin films with 10-40 nm film thickness using pulsed laser deposition (PLD). The polarisation electric-field (P-E) measurements revealed enhancements in the ferroelectric characteristics of BaTiO₃, with polarisation values (P_r ~ 10-18 µC/cm²) that are competitive with epitaxial BaTiO₃ thin films at these thicknesses. Polarisation enhancement mechanisms are linked to oxygen content, strain, and crystal quality.<br/>These findings provide new insights into the scaling of perovskite ferroelectrics and open up new opportunities for integrating perovskite materials into CMOS technologies.<br/><br/>References:<br/>J. F. Scott, “Overview,” in <i>Ferroelectric Random-Access Memories: Fundamentals and Applications</i>, H. Ishiwara, M. Okuyama, and Y. Arimoto, Eds. Springer Berlin Heidelberg, 2004, pp. 3–16<br/>J. Junquera and P. Ghosez, “Critical thickness for ferroelectricity in perovskite ultrathin films,” <i>Nature</i>, vol. 422, no. 6931, pp. 506–509, Apr. 2003<br/>Y. S. Kim <i>et al.</i>, “Critical thickness of ultrathin ferroelectric BaTiO3 films,” <i>Applied Physics Letters</i>, vol. 86, no. 10, p. 102907, Mar. 2005<br/>Y. Jiang, E. Parsonnet, A. Qualls <i>et al.</i>, “Enabling ultra-low-voltage switching in BaTiO3”<br/><i>Nature Materials</i> 21, 779–785, May 2022