Low-energy switching of ferroelectrics has been intensively studied for energy-efficient nanoelectronics. Mechanical force is considered as a low-energy consumption technique for switching the polarization of ferroelectric films due to the flexoelectric effect. Reduced threshold force is always desirable for the considerations of energy saving, easy domain manipulation, and sample surface protection. In this work, the mechanical switching behaviors of BaTiO3/SrRuO3 epitaxial heterostructure grown on Nb:SrTiO3 (001) substrate are reported. Domain switching is found to be induced by an extremely low tip force of 320 nN (estimated pressure ∼0.09 GPa), which is the lowest value ever reported. This low mechanical threshold is attributed to the small compressive strain, the low oxygen vacancy concentration in BaTiO3 film, and the high conductivity of the SrRuO3 electrode. The flexoelectricity under both perpendicular mechanical load (point measurement) and sliding load (scanning measurement) are investigated. The sliding mode shows a much stronger flexoelectric field for its strong trailing field. The mechanical written domains show several advantages in comparison with the electrically written ones: low charge injection, low energy consumption, high density, and improved stability. The ultralow-pressure switching in this work presents opportunities for next-generation low-energy and high-density memory electronics.
Keywords: compressive strain; ferroelectrics; flexoelectric; mechanical switching; ultralow mechanical force.