Piezoelectric and Dielectric Enhancement in Orientation-Engineered Freestanding Epitaxial Ba(Ti,Sn)O₃ Membranes

Heterogeneous integration of freestanding single-crystalline ferroelectric membranes offers a promising route to leverage their dielectric, piezoelectric, and nonlinear optical behavior in adaptive electronics. Crystallographic orientation engineering in these membranes further enables tuning of strain states, domain characteristics, and resulting functional properties. While orientation-engineered Pb-based piezoelectric membranes have been demonstrated, similar studies on Pb-free systems remain limited. Here, single-crystalline BaTi_0.97Sn_0.03O₃ (BST) membranes along three different crystallographic orientations are fabricated via an epitaxial layer lift-off process on Indium Tin oxide (ITO)-coated glass substrates to investigate the anisotropic dielectric, piezoelectric, and ferroelectric properties. Relaxation of substrate-induced compressive strain promotes enhanced in-plane and out-of-plane domain nucleation, yielding superior piezoelectric and dielectric responses across all orientations. An enhanced piezoelectric response in all BST membranes (61-113 pm/V) is observed. Dielectric analysis further reveals a significant enhancement in permittivity for all the freestanding membranes compared to their clamped counterparts, at frequencies above ∼10⁵ Hz (∼150 at 5 MHz), indicating faster polarization relaxation dynamics. Overall, this study demonstrates the influence of crystallographic orientation on domain evolution in freestanding membranes and paves the way for their integration into next-generation high-frequency dielectric and microelectromechanical devices.