ABSTRACT The development of microwave photonics requires monolithic integration of functional thin‐film layers on low‐loss substrates, but epitaxial film growth is limited to materials with compatible crystal structure and chemistry, hindering the flexibility of device design. Herein, high‐quality epitaxial BaTiO 3 thin films are fabricated onto low‐loss, non‐perovskite substrates, including sapphire and amorphous fused silica, via a flexible freestanding SrTiO 3 template strategy. Templated growth on SrTiO 3 membranes results in highly aligned in‐plane polarization and well‐defined domain switching characteristics in BaTiO 3 thin films, leading to an effective Pockels coefficient of 202 pm/V and a dielectric tunability up to ∼30% at 110 GHz. The Cole‐Cole modeling analysis further reveals a bias‐dependent relaxation behavior bridging high‐frequency polarization modes with domain wall dynamics. By overcoming lattice mismatch and thermal expansion constraints of heteroepitaxial growth on rigid substrates, this freestanding template approach provides a versatile and potentially scalable strategy for monolithic integration of BaTiO 3 films, enabling high‐performance multifunctional microwave photonic systems.
Ma et al. (Tue,) studied this question.
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