Electrically Controllable Kirigami Structures in Free-Standing Ferroelectric Thin Films

Based on phenomenological Landau-Ginzburg theory, ferroelectric polarizations and elastic strains are correlated each other. This provides opportunities to control mechanical configurations and properties by tuning ferroelectric domain profiles in the materials using electric field. However, in bulk crystals or thin films, this effect is highly diminished because of the substrate clamping, i.e fixed strain condition. In contrast, in free-standing ferroelectric films where substrate clamping doesn't exist, ferroelectric polarizations immediately react to the external stimuli and realign their directions accordingly, changing the strain profile in the film. This results in extraordinary mechanical and electrical properties such as superelasticity, shape memory effect, and giant piezoelectric response in free-standing films [1,2]. Here, we present nano- and micro- kirigami structures in ferroelectric BaTiO3 free-standing thin films where kirigami configurations are electrically controllable. Epitaxial BaTiO3 (BTO) films were deposited on MgO substrate using physical vapor deposition method and kirigami shapes were patterned onto the films via photo(e-beam)-lithography and dry/wet etching techniques. When electron beam or electric field is applied to the structures, ferroelectric polarizations in BTO film re-oriented accordingly and altered the strain profile in kirigami structures. As a result, depending on the beam dose or electric field intensity, the change in kirigami configurations including curvature and height were controllable. We believe that this technique could pave the new way for fabricating complex structures for various electrical and optical applications, such as reconfigurable metasurfaces with tunable optical properties or MEMS structures for electro-sensitive force sensors.<br/>References<br/>[1] G. Dong<i> et al.</i>, Super-elastic ferroelectric single-crystal membrane with continuous electric dipole rotation. <i>Science</i> <b>366</b>, 475-479 (2019).<br/>[2] H. Elangovan<i> et al.</i>, Giant Superelastic Piezoelectricity in Flexible Ferroelectric BaTiO3 Membranes. <i>ACS Nano</i> <b>14</b>, 5053-5060 (2020).