Critical thickness of ultrathin ferroelectric BaTi O3 films

To investigate the critical thickness of ferroelectric BaTi O3 (BTO) films, we fabricated fully strained SrRu O3 BTOSrRu O3 heterostructures on SrTi O3 substrates by pulsed laser deposition with in situ reflection high-energy electron diffraction. We varied the BTO layer thickness from 3 to 30 nm. By fabricating 10×10 μ m2 capacitors, we could observe polarization versus electric-field hysteresis loops, which demonstrate the existence of ferroelectricity in BTO layers thicker than 5 nm. This observation provides an experimental upper bound of 5 nm for the critical thickness. The BTO thickness-dependent scaling of the remanent polarization agrees with the predictions of recent first-principle simulations [J. Junquera and P. Ghosez, Nature 422, 506 (2003)].